Piper chaba Hunter (Piperaceae) is a common pepper in the southern part of Bangladesh. Various pa... more Piper chaba Hunter (Piperaceae) is a common pepper in the southern part of Bangladesh. Various parts of this plant have been extensively used in different traditional formulations including ayurveda. In order to rationalize the ethnomedical uses of this plant in a number of ailments, the methanol extract of the stem bark was subjected to preliminary evaluation for analgesic, anti-inflammatory, diuretic, anti-diarrhoeal, effect on gastrointestinal motility and CNS depressant activity in mice and rat at 125, 250 and 500 mg/kg body weight doses. The extract at given doses significantly and dose dependently reduced the frequency of acetic acid induced writhing in mice, prolonged the tail flicking latency in mice, reduced Carrageenan-induced paw edema volume in rat, delayed the onset as well as reduced the frequency of castor oil induced diarrhoeal episodes in mice, decreased gastrointestinal motility as assessed by the charcoal motility test in mice and prolonged pentobarbitone induced sleeping time in mice. However at the same doses, the extract exhibited moderate diuretic activity only at the highest dose.
Several studies have revealed piperine and a few related compounds as potent inhibitors of monoam... more Several studies have revealed piperine and a few related compounds as potent inhibitors of monoamine oxidases without delineating the underlying mechanism. Using in silico modelling, we propose a structural basis of such activity by showing that these compounds can successfully dock into the inhibitor binding pockets of human monoamine oxidase isoforms with predicted affinities comparable to some known inhibitors. The results therefore suggest that piperine can be a promising lead for developing novel monoamine oxidase inhibitors.
Inositol-1,4,5-trisphosphate receptors (IP 3 Rs) are intracellular Ca 2+ channels that are regula... more Inositol-1,4,5-trisphosphate receptors (IP 3 Rs) are intracellular Ca 2+ channels that are regulated by IP 3 and Ca 2+ and are modulated by many additional signals. These properties allow them to initiate and, via Ca 2+ -induced Ca 2+ release, regeneratively propagate Ca 2+ signals evoked by receptors that stimulate formation of IP 3 . The ubiquitous expression of IP 3 R highlights their importance, but it also presents problems when attempting to resolve the behavior of defined IP 3 R. DT40 cells are a pre-B-lymphocyte cell line in which high rates of homologous recombination afford unrivalled opportunities to disrupt endogenous genes. DT40knockout cells with both alleles of each of the three IP 3 R genes disrupted provide the only null-background for analysis of homogenous recombinant IP 3 R. We review the properties of DT40 cells and consider three areas where they have contributed to understanding IP 3 R behavior. Patch-clamp recording from the nuclear envelope and Ca 2+ release from intracellular stores loaded with a low-affinity Ca 2+ indicator address the mechanisms leading to activation of IP 3 R. We show that IP 3 causes intracellular IP 3 R to cluster and re-tune their responses to IP 3 and Ca 2+ , better equipping them to mediate regenerative Ca 2+ signals. Finally, we show that DT40 cells reliably count very few IP 3 R into the plasma membrane, where they mediate about half the Ca 2+ entry evoked by the B-cell antigen receptor.
Background: Inositol 1,4,5-trisphosphate receptors (IP 3 R) are expressed in almost all animal ce... more Background: Inositol 1,4,5-trisphosphate receptors (IP 3 R) are expressed in almost all animal cells. Three mammalian genes encode closely related IP 3 R subunits, which assemble into homo-or hetero-tetramers to form intracellular Ca 2 + channels. Scope of the review: In this brief review, we first consider a variety of complementary methods that allow the links between IP 3 binding and channel gating to be defined. How does IP 3 binding to the IP 3 -binding core in each IP 3 R subunit cause opening of a cation-selective pore formed by residues towards the C-terminal? We then describe methods that allow IP 3 , Ca 2 + signals and IP 3 R mobility to be examined in intact cells. A final section briefly considers genetic analyses of IP 3 R signalling. Major conclusions: All IP 3 R are regulated by both IP 3 and Ca 2 + . This allows them to initiate and regeneratively propagate intracellular Ca 2 + signals. The elementary Ca 2 + release events evoked by IP 3 in intact cells are mediated by very small numbers of active IP 3 R and the Ca 2 + -mediated interactions between them. The spatial organization of these Ca 2 + signals and their stochastic dependence on so few IP 3 Rs highlight the need for methods that allow the spatial organization of IP 3 R signalling to be addressed with single-molecule resolution. General significance: A variety of complementary methods provide insight into the structural basis of IP 3 R activation and the contributions of IP 3 -evoked Ca 2 + signals to cellular physiology. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.
Inositol 1,4,5-trisphosphate receptors (IP 3 R) are ubiquitous intracellular Ca 2+ channels. IP 3... more Inositol 1,4,5-trisphosphate receptors (IP 3 R) are ubiquitous intracellular Ca 2+ channels. IP 3 binding to the IP 3 -binding core (IBC) near the N-terminal initiates conformational changes that lead to opening of a pore. The mechanisms are unresolved. We synthesized 2-O-modified IP 3 analogues that are partial agonists of IP 3 R. These are like IP 3 in their interactions with the IBC, but they are less effective than IP 3 in rearranging the relationship between the IBC and N-terminal suppressor domain (SD), and they open the channel at slower rates. IP 3 R with a mutation in the SD occupying a position similar to the 2-O-substituent of the partial agonists has a reduced open probability that is similar for full and partial agonists. Bulky or charged substituents from either the ligand or SD therefore block obligatory coupling of the IBC and SD. Analysis of ΔG for ligand binding shows that IP 3 is recognised by the IBC and conformational changes then propagate entirely via the SD to the pore.
The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organizat... more The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organization of cytosolic Ca 2þ signals, most of which are generated by regulated openings of Ca 2þ -permeable channels. Most Ca 2þ channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP 3 R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca 2þ signals. All Ca 2þ channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca 2þ channels via the ER. How do cells avoid wayward activity of Ca 2þ channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca 2þ channels, IP 3
The inositol trisphosphate receptor (InsP 3 R) forms a calcium channel that resides in the membra... more The inositol trisphosphate receptor (InsP 3 R) forms a calcium channel that resides in the membrane of the endoplasmic reticulum and is activated by inositol trisphosphate (InsP 3 ). InsP 3 is a phosphorylated monosaccharide that is generated via hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, and activation of the InsP 3 R is involved in a broad range of biological processes, including cell division, apoptosis and development. Rahman et al. 1,2 reported that exposure to low concentrations of InsP 3 induces rapid clustering of InsP 3 R Ca 21 release channels normally randomly distributed in endoplasmic reticulum/ outer nuclear membranes. Importantly, clustered channels gate differently from lone channels. Using similar protocols, we observed InsP 3 R channel clustering without exposure to InsP 3 , as we found in other systems 3-5 with protocols designed to avoid InsP 3 preexposure. More significantly, we find that clustering has no effect on InsP 3 R channel gating. For this reason, we believe that InsP 3 -induced channel clustering and modification of channel gating by clustering may not be universal phenomena.
Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca ... more Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca 2+ that is tapped by the Ca 2+ -mobilizing messenger, NAADP. In this article, we review evidence that NAADP-mediated Ca 2+ release from this acidic Ca 2+ store proceeds through activation of the newly described two-pore channels (TPCs). We discuss recent advances in defining the sub-cellular targeting, topology and biophysics of TPCs. We also discuss physiological roles and the evolution of this ubiquitous ion channel family.
Inositol 1,4,5-trisphosphate receptors (IP(3)R) are ubiquitous intracellular Ca(2+) channels. The... more Inositol 1,4,5-trisphosphate receptors (IP(3)R) are ubiquitous intracellular Ca(2+) channels. They are regulated by IP(3) and Ca(2+) and can thereby both initiate local Ca(2+) release events and regeneratively propagate Ca(2+) signals evoked by receptors that stimulate IP(3) formation. Local signaling by small numbers of IP(3)R underpins the utility of IP(3)-evoked Ca(2+) signals as a ubiquitous signaling pathway. The physiological impact of Ca(2+) release by very small numbers of IP(3)R underscores the necessity to understand the behavior of IP(3)R at the single-channel level. In addition, and in common with analyses of every other ion channel, single-channel analyses have the potential to define the steps linking IP(3) binding to channel opening. Patch-clamp recording, by resolving the openings and closings of single channels with exquisite temporal resolution, is the most powerful technique for analysis of single-channel events. It has contributed enormously to the understanding of gating and desensitization/inactivation of numerous ion channels. However, most IP(3)R reside within intracellular membranes, where they are inaccessible to conventional patch-clamp recording methods. Here, we describe the application of nuclear patch-clamp methods to single-channel analyses of native and recombinant IP(3)R.
The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organizat... more The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organization of cytosolic Ca 2þ signals, most of which are generated by regulated openings of Ca 2þ -permeable channels. Most Ca 2þ channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP 3 R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca 2þ signals. All Ca 2þ channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca 2þ channels via the ER. How do cells avoid wayward activity of Ca 2þ channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca 2þ channels, IP 3
Piper chaba Hunter (Piperaceae) is a common pepper in the southern part of Bangladesh. Various pa... more Piper chaba Hunter (Piperaceae) is a common pepper in the southern part of Bangladesh. Various parts of this plant have been extensively used in different traditional formulations including ayurveda. In order to rationalize the ethnomedical uses of this plant in a number of ailments, the methanol extract of the stem bark was subjected to preliminary evaluation for analgesic, anti-inflammatory, diuretic, anti-diarrhoeal, effect on gastrointestinal motility and CNS depressant activity in mice and rat at 125, 250 and 500 mg/kg body weight doses. The extract at given doses significantly and dose dependently reduced the frequency of acetic acid induced writhing in mice, prolonged the tail flicking latency in mice, reduced Carrageenan-induced paw edema volume in rat, delayed the onset as well as reduced the frequency of castor oil induced diarrhoeal episodes in mice, decreased gastrointestinal motility as assessed by the charcoal motility test in mice and prolonged pentobarbitone induced sleeping time in mice. However at the same doses, the extract exhibited moderate diuretic activity only at the highest dose.
Several studies have revealed piperine and a few related compounds as potent inhibitors of monoam... more Several studies have revealed piperine and a few related compounds as potent inhibitors of monoamine oxidases without delineating the underlying mechanism. Using in silico modelling, we propose a structural basis of such activity by showing that these compounds can successfully dock into the inhibitor binding pockets of human monoamine oxidase isoforms with predicted affinities comparable to some known inhibitors. The results therefore suggest that piperine can be a promising lead for developing novel monoamine oxidase inhibitors.
Inositol-1,4,5-trisphosphate receptors (IP 3 Rs) are intracellular Ca 2+ channels that are regula... more Inositol-1,4,5-trisphosphate receptors (IP 3 Rs) are intracellular Ca 2+ channels that are regulated by IP 3 and Ca 2+ and are modulated by many additional signals. These properties allow them to initiate and, via Ca 2+ -induced Ca 2+ release, regeneratively propagate Ca 2+ signals evoked by receptors that stimulate formation of IP 3 . The ubiquitous expression of IP 3 R highlights their importance, but it also presents problems when attempting to resolve the behavior of defined IP 3 R. DT40 cells are a pre-B-lymphocyte cell line in which high rates of homologous recombination afford unrivalled opportunities to disrupt endogenous genes. DT40knockout cells with both alleles of each of the three IP 3 R genes disrupted provide the only null-background for analysis of homogenous recombinant IP 3 R. We review the properties of DT40 cells and consider three areas where they have contributed to understanding IP 3 R behavior. Patch-clamp recording from the nuclear envelope and Ca 2+ release from intracellular stores loaded with a low-affinity Ca 2+ indicator address the mechanisms leading to activation of IP 3 R. We show that IP 3 causes intracellular IP 3 R to cluster and re-tune their responses to IP 3 and Ca 2+ , better equipping them to mediate regenerative Ca 2+ signals. Finally, we show that DT40 cells reliably count very few IP 3 R into the plasma membrane, where they mediate about half the Ca 2+ entry evoked by the B-cell antigen receptor.
Background: Inositol 1,4,5-trisphosphate receptors (IP 3 R) are expressed in almost all animal ce... more Background: Inositol 1,4,5-trisphosphate receptors (IP 3 R) are expressed in almost all animal cells. Three mammalian genes encode closely related IP 3 R subunits, which assemble into homo-or hetero-tetramers to form intracellular Ca 2 + channels. Scope of the review: In this brief review, we first consider a variety of complementary methods that allow the links between IP 3 binding and channel gating to be defined. How does IP 3 binding to the IP 3 -binding core in each IP 3 R subunit cause opening of a cation-selective pore formed by residues towards the C-terminal? We then describe methods that allow IP 3 , Ca 2 + signals and IP 3 R mobility to be examined in intact cells. A final section briefly considers genetic analyses of IP 3 R signalling. Major conclusions: All IP 3 R are regulated by both IP 3 and Ca 2 + . This allows them to initiate and regeneratively propagate intracellular Ca 2 + signals. The elementary Ca 2 + release events evoked by IP 3 in intact cells are mediated by very small numbers of active IP 3 R and the Ca 2 + -mediated interactions between them. The spatial organization of these Ca 2 + signals and their stochastic dependence on so few IP 3 Rs highlight the need for methods that allow the spatial organization of IP 3 R signalling to be addressed with single-molecule resolution. General significance: A variety of complementary methods provide insight into the structural basis of IP 3 R activation and the contributions of IP 3 -evoked Ca 2 + signals to cellular physiology. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.
Inositol 1,4,5-trisphosphate receptors (IP 3 R) are ubiquitous intracellular Ca 2+ channels. IP 3... more Inositol 1,4,5-trisphosphate receptors (IP 3 R) are ubiquitous intracellular Ca 2+ channels. IP 3 binding to the IP 3 -binding core (IBC) near the N-terminal initiates conformational changes that lead to opening of a pore. The mechanisms are unresolved. We synthesized 2-O-modified IP 3 analogues that are partial agonists of IP 3 R. These are like IP 3 in their interactions with the IBC, but they are less effective than IP 3 in rearranging the relationship between the IBC and N-terminal suppressor domain (SD), and they open the channel at slower rates. IP 3 R with a mutation in the SD occupying a position similar to the 2-O-substituent of the partial agonists has a reduced open probability that is similar for full and partial agonists. Bulky or charged substituents from either the ligand or SD therefore block obligatory coupling of the IBC and SD. Analysis of ΔG for ligand binding shows that IP 3 is recognised by the IBC and conformational changes then propagate entirely via the SD to the pore.
The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organizat... more The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organization of cytosolic Ca 2þ signals, most of which are generated by regulated openings of Ca 2þ -permeable channels. Most Ca 2þ channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP 3 R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca 2þ signals. All Ca 2þ channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca 2þ channels via the ER. How do cells avoid wayward activity of Ca 2þ channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca 2þ channels, IP 3
The inositol trisphosphate receptor (InsP 3 R) forms a calcium channel that resides in the membra... more The inositol trisphosphate receptor (InsP 3 R) forms a calcium channel that resides in the membrane of the endoplasmic reticulum and is activated by inositol trisphosphate (InsP 3 ). InsP 3 is a phosphorylated monosaccharide that is generated via hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, and activation of the InsP 3 R is involved in a broad range of biological processes, including cell division, apoptosis and development. Rahman et al. 1,2 reported that exposure to low concentrations of InsP 3 induces rapid clustering of InsP 3 R Ca 21 release channels normally randomly distributed in endoplasmic reticulum/ outer nuclear membranes. Importantly, clustered channels gate differently from lone channels. Using similar protocols, we observed InsP 3 R channel clustering without exposure to InsP 3 , as we found in other systems 3-5 with protocols designed to avoid InsP 3 preexposure. More significantly, we find that clustering has no effect on InsP 3 R channel gating. For this reason, we believe that InsP 3 -induced channel clustering and modification of channel gating by clustering may not be universal phenomena.
Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca ... more Accumulating evidence suggests that the endo-lysosomal system provides a substantial store of Ca 2+ that is tapped by the Ca 2+ -mobilizing messenger, NAADP. In this article, we review evidence that NAADP-mediated Ca 2+ release from this acidic Ca 2+ store proceeds through activation of the newly described two-pore channels (TPCs). We discuss recent advances in defining the sub-cellular targeting, topology and biophysics of TPCs. We also discuss physiological roles and the evolution of this ubiquitous ion channel family.
Inositol 1,4,5-trisphosphate receptors (IP(3)R) are ubiquitous intracellular Ca(2+) channels. The... more Inositol 1,4,5-trisphosphate receptors (IP(3)R) are ubiquitous intracellular Ca(2+) channels. They are regulated by IP(3) and Ca(2+) and can thereby both initiate local Ca(2+) release events and regeneratively propagate Ca(2+) signals evoked by receptors that stimulate IP(3) formation. Local signaling by small numbers of IP(3)R underpins the utility of IP(3)-evoked Ca(2+) signals as a ubiquitous signaling pathway. The physiological impact of Ca(2+) release by very small numbers of IP(3)R underscores the necessity to understand the behavior of IP(3)R at the single-channel level. In addition, and in common with analyses of every other ion channel, single-channel analyses have the potential to define the steps linking IP(3) binding to channel opening. Patch-clamp recording, by resolving the openings and closings of single channels with exquisite temporal resolution, is the most powerful technique for analysis of single-channel events. It has contributed enormously to the understanding of gating and desensitization/inactivation of numerous ion channels. However, most IP(3)R reside within intracellular membranes, where they are inaccessible to conventional patch-clamp recording methods. Here, we describe the application of nuclear patch-clamp methods to single-channel analyses of native and recombinant IP(3)R.
The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organizat... more The versatility of Ca 2þ as an intracellular messenger derives largely from the spatial organization of cytosolic Ca 2þ signals, most of which are generated by regulated openings of Ca 2þ -permeable channels. Most Ca 2þ channels are expressed in the plasma membrane (PM). Others, including the almost ubiquitous inositol 1,4,5-trisphosphate receptors (IP 3 R) and their relatives, the ryanodine receptors (RyR), are predominantly expressed in membranes of the sarcoplasmic or endoplasmic reticulum (ER). Targeting of these channels to appropriate destinations underpins their ability to generate spatially organized Ca 2þ signals. All Ca 2þ channels begin life in the cytosol, and the vast majority are then functionally assembled in the ER, where they may either remain or be dispatched to other membranes. Here, by means of selective examples, we review two issues related to this trafficking of Ca 2þ channels via the ER. How do cells avoid wayward activity of Ca 2þ channels in transit as they pass from the ER via other membranes to their final destination? How and why do some cells express small numbers of the archetypal intracellular Ca 2þ channels, IP 3
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Papers by taufiq rahman