Neurotoxins (a-bungarotoxin, najatoxin, etc.), isolated from the venom of snakes of the cobra fam... more Neurotoxins (a-bungarotoxin, najatoxin, etc.), isolated from the venom of snakes of the cobra family have the property of selectively and irreversibiy bIoeking the effects of acetylehoIine. According to existing data, neurotoxins act on ceils with nicotine-sensitive eholinergic receptors [5, 7]. In some cases, however, it has been shown that not all nicotine-sensitive cells are blocked by neurotoxins. For instance, in experiments on the dorsal muscle of the leech, neurotoxins did not alter the effects of nieotinomimeties, although the choiinergic receptors of this muscle are usually regarded as typical nicotine-sensitive structures [2, 10]. Nor was sensitivity to neurotoxins found in experiments on the hearts and muscles of molIuses and echinoderms, even though these objects have similar pharmacological characteristics [3].
The potency of mono- and dikationic derivatives of adamantane and phenylcyclohexyl to prevent sei... more The potency of mono- and dikationic derivatives of adamantane and phenylcyclohexyl to prevent seizures induced in mice by intraperitoneal administration of 80 mg/kg pentylenetetrazol (corazol), was studied. Monocationic derivatives of phenylcyclohexyl, being the selective channel blockers of NMDA glutamate receptors, as well memantine and MK-801 in micromolar concentrations, prevented both clonic and tonic components of corazol-induced convulsions. Their dicatonic derivatives which are channel blockers of NMDA and AMPA types of glutamate receptors, failed to prevent clonic seizures but at submicromolar concentrations prevented the tonic extensions provoked by corazol. Evidently, convulsive action of corazol originating from suppression of GABA-ergic inhibition is realized through activation of glutamergic synaptic transmission, and NMDA receptors are mainly involved in genesis of clonic seizures whereas activation of AMPA receptors is important for the tonic component of the corazol...
Structural determinants of blocking the glutamate receptors of AMPA and NMDA subtypes, were studi... more Structural determinants of blocking the glutamate receptors of AMPA and NMDA subtypes, were studied. Close location of hydrophobic and ammonium groups is necessary for affective blocking of the NMDA receptor channels, whereas blockers of the AMPA receptor channels have a distance of about 10 angstroms between these two groups. Models of the channels meeting these topographic data have been devised using a molecular mechanics approach. The accomplished studies revealed molecular basis of channel blockade of the NMDA and AMPA receptors. This may allow designing predictable new blocking compounds with a desired selectivity.
Spontaneous miniature end-plate currents (MEPC) and acetylcholine-induced noise were recorded in ... more Spontaneous miniature end-plate currents (MEPC) and acetylcholine-induced noise were recorded in muscle fibres of m. longitudinalis linguae of lamprey. The MEPC decay time constant was 5.3 ms and amplitude 2.2 nA. The mean channel life time was 3.6 ms and conductance 13.6 pS. Ionic channels in synaptic and extrasynaptic zones had identical kinetics. Inhibition of acetylcholinesterase induced a 2.2-fold prolongation of MEPC, but did not affect the channel life time.
Numerical model showing action of open channel blockers on the neuromuscular junction is describe... more Numerical model showing action of open channel blockers on the neuromuscular junction is described. Quantitative aspects of the simple blocking action are analyzed and criteria which allow discriminating between channel blocking action and channel kinetics modification are suggested. The results of simulation are compared with experimental data. Some peculiarities of channel blocking drug action after acetylcholinesterase inhibition are discussed.
Spontaneous electric activity (mean amplitude of impulses--200-300 muV and frequency--0.0m-2.9 Hz... more Spontaneous electric activity (mean amplitude of impulses--200-300 muV and frequency--0.0m-2.9 Hz/s) was observed in isolated rabbit superior cervical symphathetic ganglia using the sucrose-gap method. This spontaneous activity was completely abolished by d-tubocurarine (5-10(-5) M) and hexamethonium (1-10(-4) M). The frequency of the spontaneous discharges was increased by doubling of osmotic pressure, increasing of [K]0 and adding theophilline or ethanol to perfusing solution. These findings suggest that the activity observed is due to spontaneous release of the transmitter by preganglionic nerve endings. However tetrodotoxin in relatively low concentrations (2.5-5-10(-7) g/ml) reversibly inhibited this activity. In high [Ca]0 solutions spontaneous discharges of an isolated ganglion were reduced or completely blocked. These facts suggest that the action potential generation mechanisms also participate in the spontaneous activity of the isolated cervical sympathetic ganglion.
Spontaneous miniature junctional potentials and induced by motor nerve stimulation junctional pot... more Spontaneous miniature junctional potentials and induced by motor nerve stimulation junctional potentials were recorded in muscle fibres of the third instar Drosophila larvae. Presynaptically active neurotoxins isolated from the snake venoms (beta-bungarotoxin 4.5 x 10(-7) M, notexin and notechis-II-51 X 10(-7) M, Crotoxin 9 x 10(-8) M, phospholipase from the venom of cobra 4 x 10(-6) M did not induce any changes in transmitter release during 60--120 min of contact with Drosophila preparation, although these concentrations exceed those used in frog or mice preparations. On the contrary, bee venom phospholipase (1.25 x 10(-7) M) turned out to be even more active than in frog or mice junctions. A similar sequence of three phases of the presynaptic blocking effect was found: initial decrease followed by a period of increase and finally -- depression of both spontaneous and evoked release. Bee venom phospholipase was ineffective in Ca2+-free solution but its irreversible binding to nerve...
Control of the length of action of medicinal substances is an important pharmacological problem. ... more Control of the length of action of medicinal substances is an important pharmacological problem. From the chemical standpoint, its successful solution would be possible with the aid of inactivators which act selectively on the medicinal substances and convert them into inactive compounds. Such substances, introduced at the right moment, would stop the action of the medicinal agent.
Pfl�gers Archiv European Journal of Physiology, 1984
Using voltage-clamp techniques spontaneously occuring miniature end-plate currents (mepc) and ner... more Using voltage-clamp techniques spontaneously occuring miniature end-plate currents (mepc) and nerveevoked end-plate currents (epc) were recorded in frog glycerol-treated or cut muscle preparations. Epcs were induced by pairs of stimuli (the delay of the 2nd stimulus, A t being 6 ms-30 s; one pair was delivered every 60-90 s). The decay time constant of the epc (zep~) was longer, the larger its quantal content despite the presence of active acetylcholinesterase (ACHE). After treatment with anticholinesterases (prostigmine or armin, an irreversible inhibitor) this increase in zepo became more pronounced. When AChE was fully active the decay of the 1st epc (~1) was slightly faster than the decay of the 2nd epc (r2) only when the interstimulus interval was rather short (A t < 20 ms). Following treatment with anticholinesterases this difference between ~2 and zl could be determined even when At was as long as 30 s. In anticholinesterase-treated preparations A~ was found to be inversely proportional to log At: a 50% increase in the decay time-constant of the 2nd epc occurred with 3t=120ms. During continuous stimulation (10 impulses/s) Z~po increased from the 1st to the 5-6th responses, but then decreased in parallel with the fall in the epc amplidude. The phenomenon of postsynaptic potentiation we observed could be readily abolished when quantal content was decreased by the presence of magnesium ions, but it was relatively unaffected when the receptor density was decreased by ~-bungarotoxin (c~-BuTX). The possible existence is discussed of two kinds of repetitive binding of ACh molecules, first, to free cholinoreceptors (a process wh/Lch could be inhibited by c~-BuTX) and, second, to a complex of the cholinoreceptor plus one molecule of ACh (a process which is less sensitive to e-BuTX blocking action).
Pfl�gers Archiv European Journal of Physiology, 1982
Miniature end-plate currents (mepcs) were recorded from fast and slow muscle fibres in two muscle... more Miniature end-plate currents (mepcs) were recorded from fast and slow muscle fibres in two muscles, m. cruralis and m. ileofibularis, under voltage clamp or extracellularly. Both fibre types showed an identical sensitivity to c~bungarotoxin, and an exponential dependence of mepc decay time-constant upon membrane potential, but there were some important differences : i) the rise time and half-time of decay were approximately 3 times longer in slow junctions than in fast ones; ii) inhibition of AChE had a more prominent effect on mepcs recorded in fast fibres while preserving the significant difference in mepc time course between fast and slow fibres; iii) treatment by c~-bungarotoxin had a greater effect on mepc time course in slow junctions even in the absence of anticholinesterase; iv) a more prominent variability of mepc time course was observed in slow junctions, especially after treatment by anticholinesterase drugs. Fluctuations of conductance of the postjunctional membrane induced by application of acetylcholine to different frog muscle fibres have been analysed. The autocorrelation function of these fluctuations was exponential and gave information about the mean lifetime of single ionic channels and their conductance. There were two main classes of ionic channels : "fast" with mean lifetime 2.9 ms and conductance 18.3pS in single-innervated fast muscle fibres of phasic bundle of m. ileofibularis, m. sartorius and m. cutaneous pectoris; and "slow"-8.3 ms and 12.5 pS correspondingly (t = 8-10~ holding potential-80mV) in multi-innervated fibres of tonic bundle of m. ileofibularis. An intermediate type of singly-innervated muscle fibres was found in tonic bundles of m. cruralis and m. ileofibularis. The time course of mepcs and lifetime of ionic channels recorded in these fibres were intermediate between typical fast and slow mepcs. Simultaneous analysis ofmepcs and ACh-induced current fluctuations suggests that the decay of mepcs in typical fast fibres is governed mainly by the closing of ionic channels while the decay of most mepcs in slow fibres is substantially slower than the rate of channel closing. Evidently some additional factors may prolong the effect of ACh-quanta in slow junctions. The relationship between the functional properties of different muscle fibres and rates of sequential steps of postjunctional activation is discussed.
Neurotoxins (a-bungarotoxin, najatoxin, etc.), isolated from the venom of snakes of the cobra fam... more Neurotoxins (a-bungarotoxin, najatoxin, etc.), isolated from the venom of snakes of the cobra family have the property of selectively and irreversibiy bIoeking the effects of acetylehoIine. According to existing data, neurotoxins act on ceils with nicotine-sensitive eholinergic receptors [5, 7]. In some cases, however, it has been shown that not all nicotine-sensitive cells are blocked by neurotoxins. For instance, in experiments on the dorsal muscle of the leech, neurotoxins did not alter the effects of nieotinomimeties, although the choiinergic receptors of this muscle are usually regarded as typical nicotine-sensitive structures [2, 10]. Nor was sensitivity to neurotoxins found in experiments on the hearts and muscles of molIuses and echinoderms, even though these objects have similar pharmacological characteristics [3].
The potency of mono- and dikationic derivatives of adamantane and phenylcyclohexyl to prevent sei... more The potency of mono- and dikationic derivatives of adamantane and phenylcyclohexyl to prevent seizures induced in mice by intraperitoneal administration of 80 mg/kg pentylenetetrazol (corazol), was studied. Monocationic derivatives of phenylcyclohexyl, being the selective channel blockers of NMDA glutamate receptors, as well memantine and MK-801 in micromolar concentrations, prevented both clonic and tonic components of corazol-induced convulsions. Their dicatonic derivatives which are channel blockers of NMDA and AMPA types of glutamate receptors, failed to prevent clonic seizures but at submicromolar concentrations prevented the tonic extensions provoked by corazol. Evidently, convulsive action of corazol originating from suppression of GABA-ergic inhibition is realized through activation of glutamergic synaptic transmission, and NMDA receptors are mainly involved in genesis of clonic seizures whereas activation of AMPA receptors is important for the tonic component of the corazol...
Structural determinants of blocking the glutamate receptors of AMPA and NMDA subtypes, were studi... more Structural determinants of blocking the glutamate receptors of AMPA and NMDA subtypes, were studied. Close location of hydrophobic and ammonium groups is necessary for affective blocking of the NMDA receptor channels, whereas blockers of the AMPA receptor channels have a distance of about 10 angstroms between these two groups. Models of the channels meeting these topographic data have been devised using a molecular mechanics approach. The accomplished studies revealed molecular basis of channel blockade of the NMDA and AMPA receptors. This may allow designing predictable new blocking compounds with a desired selectivity.
Spontaneous miniature end-plate currents (MEPC) and acetylcholine-induced noise were recorded in ... more Spontaneous miniature end-plate currents (MEPC) and acetylcholine-induced noise were recorded in muscle fibres of m. longitudinalis linguae of lamprey. The MEPC decay time constant was 5.3 ms and amplitude 2.2 nA. The mean channel life time was 3.6 ms and conductance 13.6 pS. Ionic channels in synaptic and extrasynaptic zones had identical kinetics. Inhibition of acetylcholinesterase induced a 2.2-fold prolongation of MEPC, but did not affect the channel life time.
Numerical model showing action of open channel blockers on the neuromuscular junction is describe... more Numerical model showing action of open channel blockers on the neuromuscular junction is described. Quantitative aspects of the simple blocking action are analyzed and criteria which allow discriminating between channel blocking action and channel kinetics modification are suggested. The results of simulation are compared with experimental data. Some peculiarities of channel blocking drug action after acetylcholinesterase inhibition are discussed.
Spontaneous electric activity (mean amplitude of impulses--200-300 muV and frequency--0.0m-2.9 Hz... more Spontaneous electric activity (mean amplitude of impulses--200-300 muV and frequency--0.0m-2.9 Hz/s) was observed in isolated rabbit superior cervical symphathetic ganglia using the sucrose-gap method. This spontaneous activity was completely abolished by d-tubocurarine (5-10(-5) M) and hexamethonium (1-10(-4) M). The frequency of the spontaneous discharges was increased by doubling of osmotic pressure, increasing of [K]0 and adding theophilline or ethanol to perfusing solution. These findings suggest that the activity observed is due to spontaneous release of the transmitter by preganglionic nerve endings. However tetrodotoxin in relatively low concentrations (2.5-5-10(-7) g/ml) reversibly inhibited this activity. In high [Ca]0 solutions spontaneous discharges of an isolated ganglion were reduced or completely blocked. These facts suggest that the action potential generation mechanisms also participate in the spontaneous activity of the isolated cervical sympathetic ganglion.
Spontaneous miniature junctional potentials and induced by motor nerve stimulation junctional pot... more Spontaneous miniature junctional potentials and induced by motor nerve stimulation junctional potentials were recorded in muscle fibres of the third instar Drosophila larvae. Presynaptically active neurotoxins isolated from the snake venoms (beta-bungarotoxin 4.5 x 10(-7) M, notexin and notechis-II-51 X 10(-7) M, Crotoxin 9 x 10(-8) M, phospholipase from the venom of cobra 4 x 10(-6) M did not induce any changes in transmitter release during 60--120 min of contact with Drosophila preparation, although these concentrations exceed those used in frog or mice preparations. On the contrary, bee venom phospholipase (1.25 x 10(-7) M) turned out to be even more active than in frog or mice junctions. A similar sequence of three phases of the presynaptic blocking effect was found: initial decrease followed by a period of increase and finally -- depression of both spontaneous and evoked release. Bee venom phospholipase was ineffective in Ca2+-free solution but its irreversible binding to nerve...
Control of the length of action of medicinal substances is an important pharmacological problem. ... more Control of the length of action of medicinal substances is an important pharmacological problem. From the chemical standpoint, its successful solution would be possible with the aid of inactivators which act selectively on the medicinal substances and convert them into inactive compounds. Such substances, introduced at the right moment, would stop the action of the medicinal agent.
Pfl�gers Archiv European Journal of Physiology, 1984
Using voltage-clamp techniques spontaneously occuring miniature end-plate currents (mepc) and ner... more Using voltage-clamp techniques spontaneously occuring miniature end-plate currents (mepc) and nerveevoked end-plate currents (epc) were recorded in frog glycerol-treated or cut muscle preparations. Epcs were induced by pairs of stimuli (the delay of the 2nd stimulus, A t being 6 ms-30 s; one pair was delivered every 60-90 s). The decay time constant of the epc (zep~) was longer, the larger its quantal content despite the presence of active acetylcholinesterase (ACHE). After treatment with anticholinesterases (prostigmine or armin, an irreversible inhibitor) this increase in zepo became more pronounced. When AChE was fully active the decay of the 1st epc (~1) was slightly faster than the decay of the 2nd epc (r2) only when the interstimulus interval was rather short (A t < 20 ms). Following treatment with anticholinesterases this difference between ~2 and zl could be determined even when At was as long as 30 s. In anticholinesterase-treated preparations A~ was found to be inversely proportional to log At: a 50% increase in the decay time-constant of the 2nd epc occurred with 3t=120ms. During continuous stimulation (10 impulses/s) Z~po increased from the 1st to the 5-6th responses, but then decreased in parallel with the fall in the epc amplidude. The phenomenon of postsynaptic potentiation we observed could be readily abolished when quantal content was decreased by the presence of magnesium ions, but it was relatively unaffected when the receptor density was decreased by ~-bungarotoxin (c~-BuTX). The possible existence is discussed of two kinds of repetitive binding of ACh molecules, first, to free cholinoreceptors (a process wh/Lch could be inhibited by c~-BuTX) and, second, to a complex of the cholinoreceptor plus one molecule of ACh (a process which is less sensitive to e-BuTX blocking action).
Pfl�gers Archiv European Journal of Physiology, 1982
Miniature end-plate currents (mepcs) were recorded from fast and slow muscle fibres in two muscle... more Miniature end-plate currents (mepcs) were recorded from fast and slow muscle fibres in two muscles, m. cruralis and m. ileofibularis, under voltage clamp or extracellularly. Both fibre types showed an identical sensitivity to c~bungarotoxin, and an exponential dependence of mepc decay time-constant upon membrane potential, but there were some important differences : i) the rise time and half-time of decay were approximately 3 times longer in slow junctions than in fast ones; ii) inhibition of AChE had a more prominent effect on mepcs recorded in fast fibres while preserving the significant difference in mepc time course between fast and slow fibres; iii) treatment by c~-bungarotoxin had a greater effect on mepc time course in slow junctions even in the absence of anticholinesterase; iv) a more prominent variability of mepc time course was observed in slow junctions, especially after treatment by anticholinesterase drugs. Fluctuations of conductance of the postjunctional membrane induced by application of acetylcholine to different frog muscle fibres have been analysed. The autocorrelation function of these fluctuations was exponential and gave information about the mean lifetime of single ionic channels and their conductance. There were two main classes of ionic channels : "fast" with mean lifetime 2.9 ms and conductance 18.3pS in single-innervated fast muscle fibres of phasic bundle of m. ileofibularis, m. sartorius and m. cutaneous pectoris; and "slow"-8.3 ms and 12.5 pS correspondingly (t = 8-10~ holding potential-80mV) in multi-innervated fibres of tonic bundle of m. ileofibularis. An intermediate type of singly-innervated muscle fibres was found in tonic bundles of m. cruralis and m. ileofibularis. The time course of mepcs and lifetime of ionic channels recorded in these fibres were intermediate between typical fast and slow mepcs. Simultaneous analysis ofmepcs and ACh-induced current fluctuations suggests that the decay of mepcs in typical fast fibres is governed mainly by the closing of ionic channels while the decay of most mepcs in slow fibres is substantially slower than the rate of channel closing. Evidently some additional factors may prolong the effect of ACh-quanta in slow junctions. The relationship between the functional properties of different muscle fibres and rates of sequential steps of postjunctional activation is discussed.
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Papers by Lev Magazanik