It has been shown previously that for constant magnetic field gradients, constant velocity flow l... more It has been shown previously that for constant magnetic field gradients, constant velocity flow leads to even-echo rephasing for all echo delay times. We show that for flow which is not pluglike, even-echo rephasing also occurs for the pulsed readout gradients used in magnetic resonance imaging if and only if the gradients begin at the time the 90" pulse is applied. We also show for these gradients that even-echo rephasing for all echo delay times in the case of nonpluglike flow implies a constant flow velocity at the point considered. Furthermore, it suffices to assume the vanishing of the spin-echo phase for any even echo, since the vanishing of any even echo for all echo delay times implies that all other even echoes also vanish identically. The odd echoes are then all equal to each other and proportional to the flow velocity. If acceleration is present, it may then be seen that for nonpluglike flow, even-echo rephasing may only be present for some but not all echo delay times. However, for the typical slice selection gradients used in magnetic resonance imaging or for usual readout gradients starting after the 90" pulse is applied, it is shown that for constant velocity flow the even-echo phases do not vanish identically. Hence, rephasing cannot always occur for nonpluglike flow in either of these situations. Furthermore, the spin-echo phases are proportional to the flow velocity. The converse is also shown; namely, if the phase of any even echo at a given point is proportional to the velocity at the point considered for all echo delay times, then the flow velocity is constant at that point. Furthermore, the phases of all even echoes are also equal to each other and proportional to the flow velocity at that point. In addition, the odd echoes are then also equal to each other and proportional to the flow velocity, but with a proportionality constant different from that of the even echoes.
Aim: Reperfusion after myocardial ischemia causes cellular injury, in part due to changes in mito... more Aim: Reperfusion after myocardial ischemia causes cellular injury, in part due to changes in mitochondrial Ca2+ handling, oxidative stress, and myocyte energetics. We have previously shown that the 18-kDa translocator protein of the outer mitochondrial membrane (TSPO) can modulate Ca2+ handling. Here, we aim to evaluate the role of the TSPO in ischemia/reperfusion (I/R) injury.Methods: Rabbit ventricular myocytes underwent simulated acute ischemia (20 min) and reperfusion (at 15 min, 1 h, and 3 h) in the absence and presence of 50 μM PK11195, a TSPO inhibitor. Cell death was measured by lactate dehydrogenase (LDH) assay, while changes in mitochondrial Ca2+, membrane potential (ΔΨm), and reactive oxygen species (ROS) generation were monitored using confocal microscopy in combination with fluorescent indicators. Substrate utilization was measured with Biolog mitochondrial plates.Results: Cell death was increased by ~200% following I/R compared to control untreated ventricular myocytes...
American Journal of Physiology-Heart and Circulatory Physiology, 1991
This study determined whether the rapidity of myocardial metabolic and contractile recovery after... more This study determined whether the rapidity of myocardial metabolic and contractile recovery after brief coronary occlusion depends upon the intensity of reactive hyperemia. We also tested the hypothesis that coronary flow rate modulates contractility after brief myocardial ischemia, independent of changes in phosphorus metabolites. Eight open-chest pigs were studied with phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy with 14 s time resolution. After a 29-s anterior descending coronary occlusion, peak Doppler coronary flow velocity was alternately unrestricted (normal hyperemia, 443 +/- 40% of control) or limited to 159 +/- 9% of control. During 29 s coronary occlusion, phosphocreatine-to-inorganic phosphate ratio (PCr/Pi) and systolic segment shortening in the ischemic region fell to 28 +/- 4 and 7 +/- 7% of control, respectively. With normal hyperemia, PCr/Pi and segment shortening recovered within 29 s. With blunted hyperemia, recovery of both parameters was delayed a...
American Journal of Physiology-Heart and Circulatory Physiology, 1990
This study used 31P nuclear magnetic resonance (NMR) spectroscopy to determine whether the magnit... more This study used 31P nuclear magnetic resonance (NMR) spectroscopy to determine whether the magnitude and duration of myocardial reactive hyperemia (RH) reflect a commensurate derangement of myocardial high-energy phosphate (HEP) metabolism, or if coronary blood flow (CBF) and HEP metabolism are dissociated during RH. Twelve open-chest anesthetized pigs were studied during and after 24 s occlusion of the anterior descending coronary artery. CBF velocity was measured with a Doppler probe. NMR time resolution (4.8 s) was obtained by summing corresponding short blocks of data from multiple occlusions. During occlusion, phosphocreatine (PCr) declined to 65 +/- 5% (mean +/- SE) of control accompanied by increased spectral intensity of the Pi + phosphomonester region. By 20 s of reflow, HEPs had returned to control levels, but CBF was still elevated at 282 +/- 18% of control and remained elevated for an additional 53 +/- 7 s, during which 44 +/- 6% of total RH flow occurred. Therefore, the...
Heart failure (HF) is characterized by abnormal mitochondrial calcium (Ca2+) handling, energy fai... more Heart failure (HF) is characterized by abnormal mitochondrial calcium (Ca2+) handling, energy failure and impaired mitophagy resulting in contractile dysfunction and myocyte death. We have previously shown that the 18-kDa mitochondrial translocator protein of the outer mitochondrial membrane (TSPO) can modulate mitochondrial Ca2+ uptake. Experiments were designed to test the role of the TSPO in a murine pressure-overload model of HF induced by transverse aortic constriction (TAC). Conditional, cardiac-specific TSPO knockout (KO) mice were generated using the Cre-loxP system. TSPO-KO and wild-type (WT) mice underwent TAC for 8 weeks. TAC-induced HF significantly increased TSPO expression in WT mice, associated with a marked reduction in systolic function, mitochondrial Ca2+ uptake, complex I activity and energetics. In contrast, TSPO-KO mice undergoing TAC had preserved ejection fraction, and exhibited fewer clinical signs of HF and fibrosis. Mitochondrial Ca2+ uptake and energetics ...
American Journal of Physiology-Heart and Circulatory Physiology, 1998
Several studies have shown that maintenance of glycolysis limits the metabolic and functional con... more Several studies have shown that maintenance of glycolysis limits the metabolic and functional consequences of low-flow ischemia. Because diabetic animals are known to have impaired glycolytic metabolism coupled with increased flux through the aldose reductase (AR) pathway, we hypothesized that inhibition of AR would enhance glycolysis and thereby improve metabolic and functional recovery during low-flow ischemia. Hearts ( n = 12) from nondiabetic control and diabetic rats were isolated and retrograde perfused using 11 mM glucose with or without the AR inhibitor zopolrestat (1 μM). Hearts were subjected to 30 min of low-flow ischemia (10% of baseline flow) and 30 min of reperfusion.31P NMR spectroscopy was used to monitor time-dependent changes in phosphocreatine (PCr), ATP, and intracellular pH. Changes in the cytosolic redox ratio of NADH to NAD+were obtained by measuring the ratio of tissue lactate to pyruvate. Effluent lactate concentrations and oxygen consumption were determined...
American Journal of Physiology-Heart and Circulatory Physiology, 1999
Myocardial ischemia results in an increase in intracellular sodium concentration ([Na]i), which m... more Myocardial ischemia results in an increase in intracellular sodium concentration ([Na]i), which may lead to cellular injury via cellular swelling and calcium overload. Because protein kinase C (PKC) has been shown to reduce Na-K-ATPase activity, we postulated that pharmacological inhibition of PKC would directly increase Na-K-ATPase activity, reduce [Na]iduring ischemia, and provide protection from ischemic injury. Isolated rat hearts were subjected to 30 min of global ischemia with and without the specific PKC inhibitor chelerythrine. Intracellular pH, ATP, and [Na]iwere assessed using31P and23Na NMR spectroscopy, whereas Na-K-ATPase and PKC activity were determined using biochemical assays. Na/H exchanger activity was determined using the ammonium prepulse technique under nonischemic conditions. Chelerythrine increased Na-K-ATPase activity (13.76 ± 0.89 vs. 10.89 ± 0.80 mg ADP ⋅ h−1⋅ mg protein−1; P = 0.01), reduced PKC activity in both the membrane and cytosolic fractions (39% an...
American Journal of Physiology-Heart and Circulatory Physiology, 2001
Diabetes increases both the incidence of cardiovascular disease and complications of myocardial i... more Diabetes increases both the incidence of cardiovascular disease and complications of myocardial infarction and heart failure. Studies using diabetic animals have shown that changes in myocardial sodium transporters result in alterations in intracellular sodium (Nai) homeostasis. Because the changes in sodium homeostasis can be due to increased entry of Na+via the electroneutral Na+-K+-2Cl−cotransporter (NKCC), we conducted experiments in acute diabetic hearts to determine if 1) net inward cation flux via NKCC is increased, 2) this cotransporter contributes to a greater increase in Naiduring ischemia, and 3) inhibition of NKCC limits injury and improves function after ischemia-reperfusion. These issues were investigated in perfused type I diabetic and nondiabetic rat hearts subjected to ischemia and 60 min of reperfusion. A group of diabetic and nondiabetic hearts was perfused with 5 μM of bumetanide, an inhibitor of NKCC. Flux via NKCC, Nai, and ATP was measured in each group with t...
American Journal of Physiology-Heart and Circulatory Physiology, 2001
Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca2... more Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca2+]i), which is thought to play a critical role in ischemia-reperfusion injury. Ischemic preconditioning (PC) improves myocardial function during ischemia-reperfusion, a process that may involve opening mitochondrial ATP-sensitive potassium (KATP) channels. Because pharmacological limitation of mitochondrial calcium concentration ([Ca2+]m) overload during ischemia-reperfusion has been shown to improve myocardial function, we hypothesized that PC would reduce [Ca2+]mduring ischemia-reperfusion and that this effect was mediated by opening mitochondrial KATPchannels. Isolated rat hearts were subjected to 25 min of global ischemia and 30 min of reperfusion with or without PC in the presence of mitochondrial KATPchannel opening (diazoxide, 100 μM) and blockade [5-hydroxydecanoic acid (5-HD), 100 μM]. Contracture during ischemia (end-diastolic pressure) and functional recovery on reperfusion (d...
Generation of reactive oxygen species (ROS) is associated with cardioprotection imparted by ische... more Generation of reactive oxygen species (ROS) is associated with cardioprotection imparted by ischemic preconditioning (IPC) and pharmacological PC (PPC). The authors have previously shown that IPC or PPC, using the mitochondrial ATP-sensitive K(+) channel opener diazoxide (DZ), reduce mitochondrial Ca(2+) ([Ca(2+)](m)) during ischemia and reperfusion. To test the hypothesis that both IPC and PPC (using DZ) lead to reduced [Ca(2+)](m) and improved functional recovery via a ROS-dependent mechanism. Intracellular Ca(2+) ([Ca(2+)](i)) and [Ca(2+)](m) were measured in isolated perfused rat hearts loaded with the fluorescent indicator indo-1 acetoxymethyl ester. [Ca(2+)](m) was determined by quenching the cytosolic indo-1 signal using manganese before ischemia (25 min). IPC and DZ (100 muM) group hearts were studied with and without the ROS scavenger N-2-mercaptopropionyl glycine (400 muM) (2-MPG). Both IPC and DZ significantly reduced [Ca(2+)](i) and [Ca(2+)](m) on reperfusion compared wi...
Determination of the chemical shift and integral of the myocardial intracellula inorganic phospha... more Determination of the chemical shift and integral of the myocardial intracellula inorganic phosphate (Pi) resonance by 31P magnetic resonance spectroscopy (MRS) is often precluded due to a large overlapping signal from 2,3‐diphosphoglycerate (2,3‐DPG) from chamber and myocardial blood. This report demonstrates the use of radiofrequency (RF) magnetic field gradient echoes (RFGE) to eliminate signals from 2,3‐DPG in flowing blood, while retaining signals from intracellular myocardial Pi, ATP, and phosphocreatine (PCr). The ECG‐triggered 31P spectra were acquired from the myocardium of open chest pigs using a Philips Gyroscan 2‐T magnetic resonance spectrometer. A 2.5‐cm‐diameter surface coil attached to the myocardium was used to provide the RF gradient as well as for excitation and detection of signals. Optimal performance of the RFGE pulse sequence was obtained when the RF gradient pulses were centered at peak diastole or peak systole. Under these conditions, 2, 3‐DPG signals were co...
The effects of pulsatile flow on spin phases in spin-echo magnetic resonance imaging are consider... more The effects of pulsatile flow on spin phases in spin-echo magnetic resonance imaging are considered. General expressions for the spin phases of the first four echoes are derived in terms of the Fourier coefficients of flow. These expressions are valid for any timedependent acceleration and, hence, are not restricted to constant acceleration. The derived expressions are then theoretically evaluated for aortic flow and examined at different points in the cardiac cycle. Our results show that rephasing may occur at certain points in the cardiac cycle for either even or odd echoes depending upon the particular Fourier coefficients of the velocity function and the spin-echo delay time. However, even-echo rephasing is not always necessarily valid. Furthermore, the possibility of determining the flow velocities in the body with an appropriate series of imaging studies is also discussed.
Journal of the American College of Cardiology, 1987
surgical follow-up. Results from these examinations indicate that NMR-derived measurements of aor... more surgical follow-up. Results from these examinations indicate that NMR-derived measurements of aortic root diameter agree closely with echocardiographic measurements. In addition, NMR provides more complete anatomic detail than does echocardiography and can be utilized to assessand follow up virtually all patients with this syndrome.
One or more brief periods of ischemia, termed preconditioning, dramatically limits infarct size a... more One or more brief periods of ischemia, termed preconditioning, dramatically limits infarct size and reduces intracellular acidosis during subsequent ischemia, potentially via enhanced sarcolemmal proton efflux mechanisms. To test the hypothesis that preconditioning increases the functional activity of sodium-dependent proton efflux pathways, isolated rat hearts were subjected to 30 min of global ischemia with or without preconditioning. Intracellular sodium (Nai) was assessed using 23Na magnetic resonance spectroscopy, and the activity of the Na-H exchanger and Na-K-2CI cotransporter was measured by transiently exposing the hearts to an acid load (NH4CI washout). Creatine kinase release was reduced by greater than 60% in the preconditioned hearts (P < 0.05) and was associated with improved functional recovery on reperfusion. Preconditioning increased Na1 by 6.24+2.04 U, resulting in a significantly higher level of Na1 before ischemia than in the control hearts. Na, increased significantly at the onset of ischemia (8.48+1.21 vs. 2.57±0.81 U, preconditioned vs. control hearts; P < 0.01). Preconditioning did not reduce Na, accumulation during ischemia, but the decline in Na; during the first 5 min of reperfusion was significantly greater in the preconditioned than in the control hearts (13.48±+1.73 vs. 2.54+0.41 U; P < 0.001). Exposure of preconditioned hearts to ethylisopropylamiloride or bumetanide in the last reperfusion period limited in the increase in Na1 during ischemia and reduced the beneficial effects of preconditioning. After the NH4Cl prepulse, preconditioned hearts acidified significantly more than control hearts and had significantly more rapid recovery of pH (preconditioned, ApH = 0.35+0.04 U over 5 min; control, ApH = 0.15+0.02 U over 5 min). This rapid pH recovery was not affected by inhibition of the Na-K-2Cl cotransporter but was abolished by inhibition of the Na-H exchanger. These results demonstrate that preconditioning alters the kinetics of Na; accumulation during global ischemia as well as proton transport after NH4Cl washout. These observations are consistent with stimulation of the Na-K-2Cl cotransporter and Na-H exchanger by preconditioning.
Magnetic resonance spectroscopy (MRS) is a valuable tool for the study of myocardial ischemia. Ph... more Magnetic resonance spectroscopy (MRS) is a valuable tool for the study of myocardial ischemia. Phosphorus (31P) MRS can detect changes in high-energy phosphates resulting from ischemia and has been used to determine the sensitivity of metabolic changes to ischemia as well as to investigate the metabolic factors important for myocardial dysfunction. The mechanisms mediating postischemic dysfunction have been investigated using 31P MRS, as have interventions to limit metabolic and functional damage from ischemia. These investigations have laid the groundwork for human cardiac studies. While abnormalities following myocardial infarction have been shown in man, further work must be performed to reliably acquire localized spectra under conditions of ischemia.
Diabetes increases the incidence of cardiovascular disease as well as the complications of myocar... more Diabetes increases the incidence of cardiovascular disease as well as the complications of myocardial infarction. Studies using animal models of diabetes have demonstrated that the metabolic alterations occurring at the myocyte level may contribute to the severity of ischemic injury in diabetic hearts. Of the several mechanisms being investigated to understand the pathogenesis of diabetic complications, the increased metabolism of glucose via the polyol pathway has received considerable attention. Deviant metabolic regulation due to increased flux through aldose reductase in diabetic hearts may influence the ability of the myocardium to withstand ischemia insult. To determine if aldose reductase inhibition improves tolerance to ischemia, hearts from acute type I diabetic and nondiabetic control rats were isolated and retrograde perfused. Each group was exposed to 1 umol/1 zopolrestat, a specific inhibitor of aldose reductase, for 10 min, followed by 20 min of global ischemia and 60 min of reperfusion in the absence of zopolrestat. Zopolrestat reduced sorbitol levels before ischemia in diabetic hearts. The cytosolic redox state (NADH/NAD*), as measured by lactate-topyruvate ratios, was significantly lowered under baseline, ischemic, and reperfusion conditions in diabetic hearts perfused with zopolrestat. In these diabetic hearts, ATP was significantly higher in zopolrestat hearts during ischemia, as were phosphocreatine and left ventricular-developed pressure on reperfusion. Zopolrestat provided similar metabolic and functional benefits in nondiabetic hearts. Creatine kinase release was reduced by ~50% in both nondiabetic and diabetic hearts treated with zopolrestat. These data indicate that inhibition of aldose reductase activity preserves high-energy phosphates, maintains a lower cytosolic NADH/NAD* ratio, and markedly protects both diabetic and nondiabetic hearts during ischemia and reperfusion. Diabetes 46:292-300, 1997
Changes in high-energy phosphate metabolism may be important in the regulation of myocardial cont... more Changes in high-energy phosphate metabolism may be important in the regulation of myocardial contractile function during ischemia. This study sought to determine the dynamic relation between myocardial contractile function and high-energy phosphate metabolism during and following brief (24-second) coronary occlusion, when large and rapid changes in both parameters occur. Eight anesthetized, open-chest pigs were instrumented with a Doppler flow probe and occluder on the anterior descending coronary artery, segment length crystals in the anterior left ventricular wall, and a surface coil for phosphorus-31 nuclear magnetic resonance spectroscopy. Phosphorus-31 spectra were reconstructed with a 4.8-second time resolution by summing corresponding short blocks of data from multiple occlusions. Metabolic and functional parameters were unchanged during the first 4.8 seconds of occlusion. During the remainder of occlusion, phosphocreatine progressively declined to 66 +/- 3% of control, inorg...
It has been shown previously that for constant magnetic field gradients, constant velocity flow l... more It has been shown previously that for constant magnetic field gradients, constant velocity flow leads to even-echo rephasing for all echo delay times. We show that for flow which is not pluglike, even-echo rephasing also occurs for the pulsed readout gradients used in magnetic resonance imaging if and only if the gradients begin at the time the 90" pulse is applied. We also show for these gradients that even-echo rephasing for all echo delay times in the case of nonpluglike flow implies a constant flow velocity at the point considered. Furthermore, it suffices to assume the vanishing of the spin-echo phase for any even echo, since the vanishing of any even echo for all echo delay times implies that all other even echoes also vanish identically. The odd echoes are then all equal to each other and proportional to the flow velocity. If acceleration is present, it may then be seen that for nonpluglike flow, even-echo rephasing may only be present for some but not all echo delay times. However, for the typical slice selection gradients used in magnetic resonance imaging or for usual readout gradients starting after the 90" pulse is applied, it is shown that for constant velocity flow the even-echo phases do not vanish identically. Hence, rephasing cannot always occur for nonpluglike flow in either of these situations. Furthermore, the spin-echo phases are proportional to the flow velocity. The converse is also shown; namely, if the phase of any even echo at a given point is proportional to the velocity at the point considered for all echo delay times, then the flow velocity is constant at that point. Furthermore, the phases of all even echoes are also equal to each other and proportional to the flow velocity at that point. In addition, the odd echoes are then also equal to each other and proportional to the flow velocity, but with a proportionality constant different from that of the even echoes.
Aim: Reperfusion after myocardial ischemia causes cellular injury, in part due to changes in mito... more Aim: Reperfusion after myocardial ischemia causes cellular injury, in part due to changes in mitochondrial Ca2+ handling, oxidative stress, and myocyte energetics. We have previously shown that the 18-kDa translocator protein of the outer mitochondrial membrane (TSPO) can modulate Ca2+ handling. Here, we aim to evaluate the role of the TSPO in ischemia/reperfusion (I/R) injury.Methods: Rabbit ventricular myocytes underwent simulated acute ischemia (20 min) and reperfusion (at 15 min, 1 h, and 3 h) in the absence and presence of 50 μM PK11195, a TSPO inhibitor. Cell death was measured by lactate dehydrogenase (LDH) assay, while changes in mitochondrial Ca2+, membrane potential (ΔΨm), and reactive oxygen species (ROS) generation were monitored using confocal microscopy in combination with fluorescent indicators. Substrate utilization was measured with Biolog mitochondrial plates.Results: Cell death was increased by ~200% following I/R compared to control untreated ventricular myocytes...
American Journal of Physiology-Heart and Circulatory Physiology, 1991
This study determined whether the rapidity of myocardial metabolic and contractile recovery after... more This study determined whether the rapidity of myocardial metabolic and contractile recovery after brief coronary occlusion depends upon the intensity of reactive hyperemia. We also tested the hypothesis that coronary flow rate modulates contractility after brief myocardial ischemia, independent of changes in phosphorus metabolites. Eight open-chest pigs were studied with phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy with 14 s time resolution. After a 29-s anterior descending coronary occlusion, peak Doppler coronary flow velocity was alternately unrestricted (normal hyperemia, 443 +/- 40% of control) or limited to 159 +/- 9% of control. During 29 s coronary occlusion, phosphocreatine-to-inorganic phosphate ratio (PCr/Pi) and systolic segment shortening in the ischemic region fell to 28 +/- 4 and 7 +/- 7% of control, respectively. With normal hyperemia, PCr/Pi and segment shortening recovered within 29 s. With blunted hyperemia, recovery of both parameters was delayed a...
American Journal of Physiology-Heart and Circulatory Physiology, 1990
This study used 31P nuclear magnetic resonance (NMR) spectroscopy to determine whether the magnit... more This study used 31P nuclear magnetic resonance (NMR) spectroscopy to determine whether the magnitude and duration of myocardial reactive hyperemia (RH) reflect a commensurate derangement of myocardial high-energy phosphate (HEP) metabolism, or if coronary blood flow (CBF) and HEP metabolism are dissociated during RH. Twelve open-chest anesthetized pigs were studied during and after 24 s occlusion of the anterior descending coronary artery. CBF velocity was measured with a Doppler probe. NMR time resolution (4.8 s) was obtained by summing corresponding short blocks of data from multiple occlusions. During occlusion, phosphocreatine (PCr) declined to 65 +/- 5% (mean +/- SE) of control accompanied by increased spectral intensity of the Pi + phosphomonester region. By 20 s of reflow, HEPs had returned to control levels, but CBF was still elevated at 282 +/- 18% of control and remained elevated for an additional 53 +/- 7 s, during which 44 +/- 6% of total RH flow occurred. Therefore, the...
Heart failure (HF) is characterized by abnormal mitochondrial calcium (Ca2+) handling, energy fai... more Heart failure (HF) is characterized by abnormal mitochondrial calcium (Ca2+) handling, energy failure and impaired mitophagy resulting in contractile dysfunction and myocyte death. We have previously shown that the 18-kDa mitochondrial translocator protein of the outer mitochondrial membrane (TSPO) can modulate mitochondrial Ca2+ uptake. Experiments were designed to test the role of the TSPO in a murine pressure-overload model of HF induced by transverse aortic constriction (TAC). Conditional, cardiac-specific TSPO knockout (KO) mice were generated using the Cre-loxP system. TSPO-KO and wild-type (WT) mice underwent TAC for 8 weeks. TAC-induced HF significantly increased TSPO expression in WT mice, associated with a marked reduction in systolic function, mitochondrial Ca2+ uptake, complex I activity and energetics. In contrast, TSPO-KO mice undergoing TAC had preserved ejection fraction, and exhibited fewer clinical signs of HF and fibrosis. Mitochondrial Ca2+ uptake and energetics ...
American Journal of Physiology-Heart and Circulatory Physiology, 1998
Several studies have shown that maintenance of glycolysis limits the metabolic and functional con... more Several studies have shown that maintenance of glycolysis limits the metabolic and functional consequences of low-flow ischemia. Because diabetic animals are known to have impaired glycolytic metabolism coupled with increased flux through the aldose reductase (AR) pathway, we hypothesized that inhibition of AR would enhance glycolysis and thereby improve metabolic and functional recovery during low-flow ischemia. Hearts ( n = 12) from nondiabetic control and diabetic rats were isolated and retrograde perfused using 11 mM glucose with or without the AR inhibitor zopolrestat (1 μM). Hearts were subjected to 30 min of low-flow ischemia (10% of baseline flow) and 30 min of reperfusion.31P NMR spectroscopy was used to monitor time-dependent changes in phosphocreatine (PCr), ATP, and intracellular pH. Changes in the cytosolic redox ratio of NADH to NAD+were obtained by measuring the ratio of tissue lactate to pyruvate. Effluent lactate concentrations and oxygen consumption were determined...
American Journal of Physiology-Heart and Circulatory Physiology, 1999
Myocardial ischemia results in an increase in intracellular sodium concentration ([Na]i), which m... more Myocardial ischemia results in an increase in intracellular sodium concentration ([Na]i), which may lead to cellular injury via cellular swelling and calcium overload. Because protein kinase C (PKC) has been shown to reduce Na-K-ATPase activity, we postulated that pharmacological inhibition of PKC would directly increase Na-K-ATPase activity, reduce [Na]iduring ischemia, and provide protection from ischemic injury. Isolated rat hearts were subjected to 30 min of global ischemia with and without the specific PKC inhibitor chelerythrine. Intracellular pH, ATP, and [Na]iwere assessed using31P and23Na NMR spectroscopy, whereas Na-K-ATPase and PKC activity were determined using biochemical assays. Na/H exchanger activity was determined using the ammonium prepulse technique under nonischemic conditions. Chelerythrine increased Na-K-ATPase activity (13.76 ± 0.89 vs. 10.89 ± 0.80 mg ADP ⋅ h−1⋅ mg protein−1; P = 0.01), reduced PKC activity in both the membrane and cytosolic fractions (39% an...
American Journal of Physiology-Heart and Circulatory Physiology, 2001
Diabetes increases both the incidence of cardiovascular disease and complications of myocardial i... more Diabetes increases both the incidence of cardiovascular disease and complications of myocardial infarction and heart failure. Studies using diabetic animals have shown that changes in myocardial sodium transporters result in alterations in intracellular sodium (Nai) homeostasis. Because the changes in sodium homeostasis can be due to increased entry of Na+via the electroneutral Na+-K+-2Cl−cotransporter (NKCC), we conducted experiments in acute diabetic hearts to determine if 1) net inward cation flux via NKCC is increased, 2) this cotransporter contributes to a greater increase in Naiduring ischemia, and 3) inhibition of NKCC limits injury and improves function after ischemia-reperfusion. These issues were investigated in perfused type I diabetic and nondiabetic rat hearts subjected to ischemia and 60 min of reperfusion. A group of diabetic and nondiabetic hearts was perfused with 5 μM of bumetanide, an inhibitor of NKCC. Flux via NKCC, Nai, and ATP was measured in each group with t...
American Journal of Physiology-Heart and Circulatory Physiology, 2001
Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca2... more Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca2+]i), which is thought to play a critical role in ischemia-reperfusion injury. Ischemic preconditioning (PC) improves myocardial function during ischemia-reperfusion, a process that may involve opening mitochondrial ATP-sensitive potassium (KATP) channels. Because pharmacological limitation of mitochondrial calcium concentration ([Ca2+]m) overload during ischemia-reperfusion has been shown to improve myocardial function, we hypothesized that PC would reduce [Ca2+]mduring ischemia-reperfusion and that this effect was mediated by opening mitochondrial KATPchannels. Isolated rat hearts were subjected to 25 min of global ischemia and 30 min of reperfusion with or without PC in the presence of mitochondrial KATPchannel opening (diazoxide, 100 μM) and blockade [5-hydroxydecanoic acid (5-HD), 100 μM]. Contracture during ischemia (end-diastolic pressure) and functional recovery on reperfusion (d...
Generation of reactive oxygen species (ROS) is associated with cardioprotection imparted by ische... more Generation of reactive oxygen species (ROS) is associated with cardioprotection imparted by ischemic preconditioning (IPC) and pharmacological PC (PPC). The authors have previously shown that IPC or PPC, using the mitochondrial ATP-sensitive K(+) channel opener diazoxide (DZ), reduce mitochondrial Ca(2+) ([Ca(2+)](m)) during ischemia and reperfusion. To test the hypothesis that both IPC and PPC (using DZ) lead to reduced [Ca(2+)](m) and improved functional recovery via a ROS-dependent mechanism. Intracellular Ca(2+) ([Ca(2+)](i)) and [Ca(2+)](m) were measured in isolated perfused rat hearts loaded with the fluorescent indicator indo-1 acetoxymethyl ester. [Ca(2+)](m) was determined by quenching the cytosolic indo-1 signal using manganese before ischemia (25 min). IPC and DZ (100 muM) group hearts were studied with and without the ROS scavenger N-2-mercaptopropionyl glycine (400 muM) (2-MPG). Both IPC and DZ significantly reduced [Ca(2+)](i) and [Ca(2+)](m) on reperfusion compared wi...
Determination of the chemical shift and integral of the myocardial intracellula inorganic phospha... more Determination of the chemical shift and integral of the myocardial intracellula inorganic phosphate (Pi) resonance by 31P magnetic resonance spectroscopy (MRS) is often precluded due to a large overlapping signal from 2,3‐diphosphoglycerate (2,3‐DPG) from chamber and myocardial blood. This report demonstrates the use of radiofrequency (RF) magnetic field gradient echoes (RFGE) to eliminate signals from 2,3‐DPG in flowing blood, while retaining signals from intracellular myocardial Pi, ATP, and phosphocreatine (PCr). The ECG‐triggered 31P spectra were acquired from the myocardium of open chest pigs using a Philips Gyroscan 2‐T magnetic resonance spectrometer. A 2.5‐cm‐diameter surface coil attached to the myocardium was used to provide the RF gradient as well as for excitation and detection of signals. Optimal performance of the RFGE pulse sequence was obtained when the RF gradient pulses were centered at peak diastole or peak systole. Under these conditions, 2, 3‐DPG signals were co...
The effects of pulsatile flow on spin phases in spin-echo magnetic resonance imaging are consider... more The effects of pulsatile flow on spin phases in spin-echo magnetic resonance imaging are considered. General expressions for the spin phases of the first four echoes are derived in terms of the Fourier coefficients of flow. These expressions are valid for any timedependent acceleration and, hence, are not restricted to constant acceleration. The derived expressions are then theoretically evaluated for aortic flow and examined at different points in the cardiac cycle. Our results show that rephasing may occur at certain points in the cardiac cycle for either even or odd echoes depending upon the particular Fourier coefficients of the velocity function and the spin-echo delay time. However, even-echo rephasing is not always necessarily valid. Furthermore, the possibility of determining the flow velocities in the body with an appropriate series of imaging studies is also discussed.
Journal of the American College of Cardiology, 1987
surgical follow-up. Results from these examinations indicate that NMR-derived measurements of aor... more surgical follow-up. Results from these examinations indicate that NMR-derived measurements of aortic root diameter agree closely with echocardiographic measurements. In addition, NMR provides more complete anatomic detail than does echocardiography and can be utilized to assessand follow up virtually all patients with this syndrome.
One or more brief periods of ischemia, termed preconditioning, dramatically limits infarct size a... more One or more brief periods of ischemia, termed preconditioning, dramatically limits infarct size and reduces intracellular acidosis during subsequent ischemia, potentially via enhanced sarcolemmal proton efflux mechanisms. To test the hypothesis that preconditioning increases the functional activity of sodium-dependent proton efflux pathways, isolated rat hearts were subjected to 30 min of global ischemia with or without preconditioning. Intracellular sodium (Nai) was assessed using 23Na magnetic resonance spectroscopy, and the activity of the Na-H exchanger and Na-K-2CI cotransporter was measured by transiently exposing the hearts to an acid load (NH4CI washout). Creatine kinase release was reduced by greater than 60% in the preconditioned hearts (P < 0.05) and was associated with improved functional recovery on reperfusion. Preconditioning increased Na1 by 6.24+2.04 U, resulting in a significantly higher level of Na1 before ischemia than in the control hearts. Na, increased significantly at the onset of ischemia (8.48+1.21 vs. 2.57±0.81 U, preconditioned vs. control hearts; P < 0.01). Preconditioning did not reduce Na, accumulation during ischemia, but the decline in Na; during the first 5 min of reperfusion was significantly greater in the preconditioned than in the control hearts (13.48±+1.73 vs. 2.54+0.41 U; P < 0.001). Exposure of preconditioned hearts to ethylisopropylamiloride or bumetanide in the last reperfusion period limited in the increase in Na1 during ischemia and reduced the beneficial effects of preconditioning. After the NH4Cl prepulse, preconditioned hearts acidified significantly more than control hearts and had significantly more rapid recovery of pH (preconditioned, ApH = 0.35+0.04 U over 5 min; control, ApH = 0.15+0.02 U over 5 min). This rapid pH recovery was not affected by inhibition of the Na-K-2Cl cotransporter but was abolished by inhibition of the Na-H exchanger. These results demonstrate that preconditioning alters the kinetics of Na; accumulation during global ischemia as well as proton transport after NH4Cl washout. These observations are consistent with stimulation of the Na-K-2Cl cotransporter and Na-H exchanger by preconditioning.
Magnetic resonance spectroscopy (MRS) is a valuable tool for the study of myocardial ischemia. Ph... more Magnetic resonance spectroscopy (MRS) is a valuable tool for the study of myocardial ischemia. Phosphorus (31P) MRS can detect changes in high-energy phosphates resulting from ischemia and has been used to determine the sensitivity of metabolic changes to ischemia as well as to investigate the metabolic factors important for myocardial dysfunction. The mechanisms mediating postischemic dysfunction have been investigated using 31P MRS, as have interventions to limit metabolic and functional damage from ischemia. These investigations have laid the groundwork for human cardiac studies. While abnormalities following myocardial infarction have been shown in man, further work must be performed to reliably acquire localized spectra under conditions of ischemia.
Diabetes increases the incidence of cardiovascular disease as well as the complications of myocar... more Diabetes increases the incidence of cardiovascular disease as well as the complications of myocardial infarction. Studies using animal models of diabetes have demonstrated that the metabolic alterations occurring at the myocyte level may contribute to the severity of ischemic injury in diabetic hearts. Of the several mechanisms being investigated to understand the pathogenesis of diabetic complications, the increased metabolism of glucose via the polyol pathway has received considerable attention. Deviant metabolic regulation due to increased flux through aldose reductase in diabetic hearts may influence the ability of the myocardium to withstand ischemia insult. To determine if aldose reductase inhibition improves tolerance to ischemia, hearts from acute type I diabetic and nondiabetic control rats were isolated and retrograde perfused. Each group was exposed to 1 umol/1 zopolrestat, a specific inhibitor of aldose reductase, for 10 min, followed by 20 min of global ischemia and 60 min of reperfusion in the absence of zopolrestat. Zopolrestat reduced sorbitol levels before ischemia in diabetic hearts. The cytosolic redox state (NADH/NAD*), as measured by lactate-topyruvate ratios, was significantly lowered under baseline, ischemic, and reperfusion conditions in diabetic hearts perfused with zopolrestat. In these diabetic hearts, ATP was significantly higher in zopolrestat hearts during ischemia, as were phosphocreatine and left ventricular-developed pressure on reperfusion. Zopolrestat provided similar metabolic and functional benefits in nondiabetic hearts. Creatine kinase release was reduced by ~50% in both nondiabetic and diabetic hearts treated with zopolrestat. These data indicate that inhibition of aldose reductase activity preserves high-energy phosphates, maintains a lower cytosolic NADH/NAD* ratio, and markedly protects both diabetic and nondiabetic hearts during ischemia and reperfusion. Diabetes 46:292-300, 1997
Changes in high-energy phosphate metabolism may be important in the regulation of myocardial cont... more Changes in high-energy phosphate metabolism may be important in the regulation of myocardial contractile function during ischemia. This study sought to determine the dynamic relation between myocardial contractile function and high-energy phosphate metabolism during and following brief (24-second) coronary occlusion, when large and rapid changes in both parameters occur. Eight anesthetized, open-chest pigs were instrumented with a Doppler flow probe and occluder on the anterior descending coronary artery, segment length crystals in the anterior left ventricular wall, and a surface coil for phosphorus-31 nuclear magnetic resonance spectroscopy. Phosphorus-31 spectra were reconstructed with a 4.8-second time resolution by summing corresponding short blocks of data from multiple occlusions. Metabolic and functional parameters were unchanged during the first 4.8 seconds of occlusion. During the remainder of occlusion, phosphocreatine progressively declined to 66 +/- 3% of control, inorg...
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Papers by Saul Schaefer