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F Vyskocil

Publications and source records attributed to F Vyskocil.

At least 55 records · Page 3Linked to original sources
PubMed1995

The role of non-quantal release of acetylcholine in regulation of postsynaptic membrane electrogenesis.

In mammalian nerve-muscle preparations treated with an anticholinesterase, the acetylcholine (ACh) released non-quantally (NQR) reaches the postsynaptic receptors and causes a small depolarization of the membrane potential at the endplate region of the muscle fibres. Increase in quantal release potentiates the NQR and vice versa, the amplitude and the kinetic parameters of quantal miniature endplate currents (MEPCs) change during manipulation of NQR, indicating direct interaction between both types of release. Repetitive binding of ACh to postsynaptic receptors which prolongs the time course of MEPCs in anti-cholinesterase-treated endplates leads within 1-2 h to progressive desensitization in the presence of non-quantal release and to the subsequent shortening of the quantal responses. We have also investigated the effect of procedures known to modulate non-quantal acetylcholine release, on the small, but obvious, difference in the resting membrane potential between the endplate zone and other areas of the mouse muscle fibre. The resting membrane potential at the endplate zone with intact cholinesterase is more negative (by 2-4 mV) than in the endplate-free area. The experiments were performed to test the hypothesis that the hyperpolarization is caused by an electrogenic Na(+)-K+ pump operating during the action of ACh released in non-quantal form. Observations in favour of this idea are that both short-term denervation (which eliminates non-quantal but not quantal release) and ouabain abolish the local synaptic hyperpolarization and that subsequent application of low doses of ACh restores it. It follows, therefore, that the hyperpolarization is probably caused by a small but continuous ACh leakage from the nerve terminal.

Acetylcholine↗
PubMed1995

Potentiation of GABAA receptor in cultured mouse hippocampal cells by brain-derived peptide mixture cerebrolysin.

Application of Cerebrolysin (0.1 microgram per 1 ml) by a fast microperfusion system induced an inward current of 0.2 to 1 nA in all neurones from newborn mouse hippocampi held at -30 mV membrane potential. Cerebrolysin-induced currents were reduced by the GABAA antagonist bicuculline (2 microM) by 65%, by the NMDA antagonist aminophosphovaleric acid (APV, 10 microM) by 27% and by the non-NMDA antagonist cyanonitriquinoxalinedione (CNQX, 10 microM) by 20%. Cerebrolysin dialyzed through a 3.6 kD gut did not induce any transmembrane current but potentiated the response induced by GABA (10 microM) to 135%. We conclude that, in addition to amino acids which activate GABAA, NMDA and non-NMDA receptors, Cerebrolysin also contains a peptide which potentiates the GABAA receptor response.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1995

Muscle NMDA receptors regulate the resting membrane potential through NO-synthase.

The early postdenervation depolarization of rat diaphragm muscle fibres (8-10 mV) is substantially smaller (3 mV) when muscle strips are bathed with 1 mM L-glutamate (GLU) or N-methyl-D-aspartate (NMDA). The effects of GLU and NMDA are not seen in the presence of aminophosphonovaleric acid (APV), a blocker of NMDA-subtype of glutamate receptors, 5 mM Mg2+ (which blocks NMDA-controlled ion channels) and L-nitroarginine methylester (NAME), an inhibitor of NO-synthase. This indicates that NMDA-subtype of GLU receptors might be involved in the regulation of the membrane potential in muscle fibres, most probably through the NO-synthase system.

2-Amino-5-phosphonovalerate↗
PubMed1994

The effect of acetylcholine and related drugs on currents at the frog motor nerve terminal.

Acetylcholine, acetylthiocholine, carbachol, suberyldicholine, propionylcholine, succinylcholine, methylfurmethide and F 2268 were tested on motor nerve ending currents recorded with an extracellular microelectrode. The isolated and transversally cut cutaneous pectoris muscle of frog Rana ridibunda was used. Only acetylcholine and acetylthiocholine affected the spike waveforms in a concentration-dependent manner. Lower concentrations (1-6 x 10(-4) M) prolonged the inward Na+ current and increased the outward K+ current at the proximal and central parts of the nerve terminal. Most remote parts of the terminal were not affected. At 7 x 10(-4) M and higher, both drugs further prolonged the Na+ current and eliminated the K+ component of the spike. The potentiating effect of acetylcholine and acetylthiocholine on the K+ phase of nerve terminal current disappeared after treatment with tetraethylammonium and 4-aminopyridine. The effect also disappeared when synaptic cholinesterase was inhibited by the anticholinesterases or by treatment with collagenase. Reactivation of cholinesterase by dipyroxime restored the facilitating effect of acetylcholine. Choline and slight acidification to pH 6.8 did not mimic the acetylcholine action on the terminal currents. Facilitation of the K+ current by acetylcholine was not calcium-dependent. The results indicate that lower acetylcholine concentrations inhibit the delayed rectifier only, whereas 7 x 10(-4) M and higher concentrations of acetylcholine depress all outward currents of the terminal.

Acetylcholine↗
PubMed1994

Role of non-quantal acetylcholine release in surplus polarization of mouse diaphragm fibres at the endplate zone.

1. In mouse diaphragm, with intact cholinesterase (ChE), the mean value of the resting membrane potential was significantly higher (-84.8 +/- 0.3 mV; mean +/- S.E.M.) at the endplate zone than in the extrajunctional area of the muscle fibres (-82.5 +/- 0.3 mV) at 22 degrees C. 2. This hyperpolarization of about 2-3 mV at the endplate zone was abolished within 5 min by 1 x 10(-6) M ouabain, indicating that it might be caused by an electrogenic Na(+)-K+ pump. (+)-Tubocurarine (TC; 1 x 10(-5) M) had no effect on this hyperpolarization after bath application for 10-20 min. 3. Short-term denervation (4 h), a slight increase of Mg2+ in the bath of from 1 to 4 mM and application of a Ca(2+)-free solution for 60 min also led to the disappearance of the surplus polarization. All of these factors are known to eliminate TC-induced hyperpolarization in anti-ChE-treated muscles (H-effect), which is considered to be a correlate of non-quantal acetylcholine (ACh) leakage. 4. The time courses of the decline of the H-effect and surplus polarization after denervation were identical. 5. In short-term denervated muscles with intact ChE, the surplus polarization was restored by 5 x 10(-8) M ACh, which simulates the H-effect in anti-ChE-treated muscles. The presence of 1 x 10(-6) M ouabain either prevented or abolished the effect of the bath-applied ACh.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1994

Chemical modifications of melatonin receptors in chicken brain.

The membrane-bound or solubilized melatonin receptors were treated with protein-modifying agents under specific conditions and then assayed for 125I-melatonin binding in order to obtain information on amino acids present in the ligand binding domain. The reagents specific for sulfhydryl (N-ethylmaleimide and p-chloromercuribenzoate), guanidyl (phenylglyoxal), and amino groups (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid and 1-fluoro-2,4-dinitrobenzene) inhibited 125I-melatonin binding in a dose-dependent manner, and their effects were prevented by pretreatment with cold melatonin. These results suggest the presence of cysteine, arginine, and lysine residues in the melatonin binding domain. Decreased sensitivity of 125I-melatonin binding to guanine nucleotides after N-ethylmaleimide pretreatment suggests the presence of another sulfhydryl group within the coupling domain between the receptor and G protein. Tyrosine reagents tetranitromethane, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, N-acetylimidazole, and p-nitrobenzenesulfonyl fluoride also inhibited 125I-melatonin binding, and their effects were prevented by cold melatonin pretreatment; however, they were effective only at concentrations when cross-reaction with a sulfhydryl group may occur. Histidine reagent diethyl pyrocarbonate inhibited 125I-melatonin binding in a dose-dependent manner, and its action was reversed by cold melatonin. However, diethyl pyrocarbonate had a smaller effect in a solubilized receptor preparation and, therefore, it could have modified a site remote from the ligand binding site. Our data do not suggest the presence of tryptophanyl, aspartic, or glutamic residues at the ligand binding domain.

4-Chloro-7-nitrobenzofurazan↗
PubMed1993

Non-quantal release of acetylcholine affects polyneuronal innervation on developing rat muscle fibres.

The membrane potential at endplates of the rat hemidiaphragm for 9-day-old rats increases by 1.8 mV after addition of D-tubocurarine. The endplate depolarization before the addition of D-tubocurarine is considered to be due to non-quantal release (NQR) of acetylcholine (ACh). In the presence of an anticholinesterase this depolarization increased. It was further enhanced by 0.1-1.0 mM Mg2+ and reduced by 4 mM Mg2+ concentration. Thus the regulation of NQR at neuromuscular junctions of developing rat muscles is similar to that seen in adult mammalian species. The effect of NQR of Ach on neuromuscular contacts of muscle fibres from 8-9-day-old rat diaphragm and soleus muscles was studied. Pre-incubating the muscles in solutions where NQR was increased by lowering Mg2+ caused a significant (P < 0.01) reduction of neuromuscular contacts. This reduction did not occur when muscles were incubated in high Mg2+, when NQR is reduced. Increasing quantal release by high Ca2+ also caused a reduction of neuromuscular contacts. Histological examination of soleus muscle fibres treated with an anticholinesterase showed that muscles incubated in solutions with low (0.1 mM) concentrations of Mg2+ had significantly fewer neuromuscular contacts (38%) than those incubated in high concentrations of Mg2+ (61%). It is concluded that the NQR as assessed here contributes to the elimination of polyneuronal innervation during postnatal development of rat muscles.

Acetylcholine↗
PubMed1993

The effect of non-quantal acetylcholine release on quantal miniature currents at mouse diaphragm.

1. The amplitude and exponential decay time constant of miniature endplate currents (MEPCs) were measured in mouse diaphragms treated with anti-cholinesterase under conditions known to modulate non-quantal acetylcholine (ACh) release. 2. Anti-cholinesterase prolonged MEPC decay and the extent of this initial prolongation was not influenced by non-quantal release. When non-quantal release was present, the decays of MEPCs became increasingly faster over several hours. This increased decay did not occur in the absence of non-quantal release. 3. Potentiation of the non-quantal release by zero Mg2+ and 1 x 10(-5) M choline, on the other hand, led to acceleration of MEPC shortening. 4. Increase of temperature from 15 to 26 degrees C and the presence of the desensitization-promoting drug proadifen (5 x 10(-6) M) accelerated the rate of MEPC shortening. 5. These observations are consistent with increased receptor desensitization due to non-quantal release. Repetitive binding of ACh to postsynaptic receptors which prolongs the time course of MEPC in anti-cholinesterase-treated endplates leads to progressive desensitization in the presence of non-quantal release and to the subsequent shortening of the quantal responses.

Acetylcholine↗
PubMed1993

A correlation between quantal content and decay time of endplate currents in frog muscles with intact cholinesterase.

1. The relationship between quantal content and prolongation of endplate currents (EPC) was studied in the frog sartorius with intact synaptic acetylcholinesterase. 2. The prolongation of EPC was more pronounced in endplates with a higher quantal content both before and after potentiation of quantal release by 4-aminopyridine (4-AP). When the quantal content of EPC was lowered, either by high Mg2+ or repetitive stimulation, the EPC decay constant was reduced. 3. A certain critical value of about 120 quanta per nerve impulse was found, at which point the decay of EPC remained constant even through the quantal content was reduced further. 4. The reduction in both density and number of postsynaptic receptors, produced by alpha-bungarotoxin and (+)-tubocurarine led to a profound reduction in EPC decay during the progressive fall in EPC amplitude in both 4-AP-treated and -untreated endplates. Both drugs are known to produce a shortening of EPC in anti-cholinesterase (anti-ChE)-treated muscles, due to a decrease in receptor density and less frequent repetitive binding of ACh. 5. It is assumed that the prolongation of multiquantal EPC is caused by an increased ACh concentration near the receptors, which may provide the opportunity for repetitive binding even with full cholinesterase activity. The critical quantum content of about 120 might be the number of quanta at which the probability of multiple release at single active zones is increased above zero.

4-Aminopyridine↗
PubMed1992

Ouabain binding, ATP hydrolysis, and Na+,K(+)-pump activity during chemical modification of brain and muscle Na+,K(+)-ATPase.

The effects of 16 group-specific, amino acid-modifying agents were tested on ouabain binding, catalytical activity of membrane-bound (rat brain microsomal), sodium dodecyl sulfate-treated Na+,K(+)-ATPase, and Na+,K(+)-pump activity in intact muscle cells. With few exceptions, the potency of various tryptophan, tyrosine, histidine, amino, and carboxy group-oriented drugs to suppress ouabain binding and Na+,K(+)-ATPase activity correlated with inhibition of the Na+,K(+)-pump electrogenic effect. ATP hydrolysis was more sensitive to inhibition elicited by chemical modification than ouabain binding (membrane-bound or isolated enzyme) and than Na+,K(+)-pump activity. The efficiency of various drugs belonging to the same "specificity" group differed markedly. Tyrosine-oriented tetranitromethane was the only reagent that interfered directly with the cardiac receptor binding site as its inhibition of ouabain binding was completely protected by ouabagenin preincubation. The inhibition elicited by all other reagents was not, or only partially, protected by ouabagenin. It is surprising that agents like diethyl pyrocarbonate (histidine groups) or butanedione (arginine groups), whose action should be oriented to amino acids not involved in the putative ouabain binding site (represented by the -Glu-Tyr-Thr-Trp-Leu-Glu- sequence), are equally effective as agents acting on amino acids present directly in the ouabain binding site. These results support the proposal of long-distance regulation of Na+,K(+)-ATPase active sites.

Adenosine Triphosphate↗
PubMed1992

Comparison of two approaches to measurement of electrical impedance of glass microelectrodes designed for evaluation of temperature changes in biological tissues.

We proposed a temperature sensitive microelectrode for rapid measurements of temperature at the cellular level. In principle, the electrical impedance of the tip of the microelectrode changes with temperature. We designed an impulse measurement system (STEP) sensitive to the above changes of impedance. The system is based on a presettable negative input impedance of the current to a voltage converter. We compared the efficiency of the new STEP with the currently used RAMP system. We found following advantages of the STEP system: i) the danger of high voltage oscillations which could mechanically destroy the microelectrode tip is eliminated; ii) this system provides the opportunity to set the maximum sensitivity of the system according to the measured temperature interval. Moreover, the STEP method makes it possible to measure the resistance by using a sinusoidal stimulation signal which has to be preliminarily compensated by a rectangular signal. The shortest sampling period of the new system represents 0.1 ms with a resolution higher than 0.1 K and sensitivity better than 30 mV/K.

Animals↗
PubMed1992

Non-quantal acetylcholine release after cholinesterase inhibition in vivo.

After anticholinesterase treatment in vivo, depolarization of the postsynaptic muscle fibre membrane by about 4 mV develops due to non-quantally released acetylcholine from the motor nerve terminal. This conclusion was supported by experiments with the curarization of diaphragm slices from anticholinesterase treated mice during intracellular microelectrode recordings.

Acetylcholine↗
PubMed1991

Temperature dependence of carbachol-induced modulation of miniature end-plate potential frequency in rats.

In the rat soleus, the frequency of miniature end-plate potentials (MEPP) did not change after application of 10(-5) M of the cholinomimetic drug carbachol between 18 degrees C and 34 degrees C but decreased by 40% at physiological temperatures of 37-38 degrees C. The carbachol-induced decrease in MEPP frequency was not eliminated by 10(-7) to 10(-8) M atropine or 3 x 10(-7) (+)-tubocurarine similarly as had been previously found at frog neuromuscular junction.

Animals↗
PubMed1991

Kinetic differences in the effect of calcium on quantal and non-quantal acetylcholine release at the murine diaphragm.

The effects of Ca2+ withdrawal on non-quantal, evoked quantal and spontaneous quantal release of acetylcholine (ACh) from the motor nerve terminals were studied with standard intracellular recording techniques. Anticholinesterase-treated mouse diaphragms were used. In a Ca2(+)-free solution all forms of ACh release decreased, but with different kinetics. As expected, evoked quantal release declined to zero within a few minutes. Spontaneous quantal release, i.e. the frequency of the miniature end-plate potentials (MEPPs), decreased to 15% of the control within 20 min after calcium withdrawal. The slowest decay was that of non-quantal release which declined very slowly and reached zero after 45-50 min. Following Ca2+ re-admission, both quantal types of ACh release were rapidly restored (evoked in 10 min, spontaneous in 20 min). However, recovery of non-quantal release did not occur until after 50 to 60 min.

Acetylcholine↗
PubMed1991

The dependence of non-quantal acetylcholine release on the choline-uptake system in the mouse diaphragm.

The time course of local end-plate hyperpolarization after d-tubocurarine application measured by an intracellular microelectrode was followed in vitro in anticholinesterase-treated mouse diaphragm pinned to the bottom of the perfusion chamber. The d-tubocurarine-induced hyperpolarization, which served as an indicator of non-quantal acetylcholine release, started to decline from 6 mV after 1 h and was negligible after 3 h in continuously perfused preparations. This decline was slowed down by 10 mumol l-1 choline and almost completely prevented by long-term nerve stimulation with a frequency of 3 Hz. The rapid decrease of the d-tubocurarine-induced hyperpolarization was observed within 10-15 min after the application of 1 mumol l-1 hemicholinium-3 and substitution of lithium for sodium. Both these procedures inhibit the fast choline uptake into nerve terminals. Our data suggest that the amount of available acetylcholine for non-quantal release is proportional to the rate of its synthesis and to the number of available carriers in the nerve terminals. Some of our observations might also be explained by postulating that the choline-uptake system as such is responsible for the non-quantal release.

Acetylcholine↗
PubMed1991

Depression of miniature endplate potential frequency by acetylcholine and its analogues in frog.

1. Acetylcholine (ACh), 7.5 x 10(-5) M, and carbachol, 5 x 10(-6) M (CCh) depressed the frequency of miniature endplate potentials (m.e.p.ps) in the frog (Rana temporaria) sartorius neuromuscular junction with active acetylcholinesterase to about 50-55% of the controls. 2. A similar depression was produced by the nicotinic agonists, nicotine, suberyldicholine and tetramethylammonium. 3. The muscarinic agonists, oxotremorine, methylfurmethide and methacholine were without effect on m.e.p.p. frequency. The muscarinic antagonist, atropine and the nicotinic antagonist, (+)-tubocurarine, had no effect on the depression of m.e.p.p. frequency evoked by CCh. 4. The ganglionic blockers, benzhexonium and IEM-1119, were also without effect on the CCh-evoked depression of m.e.p.p. frequency. 5. Pretreatment of muscles with anticholinesterases did not prevent the CCh-induced drop in m.e.p.p. frequency. 6. The effect of CCh was proportionally the same as in the controls in preparations where the m.e.p.p. frequency was changed by elevation of K+ and in the presence of theophylline, noradrenaline, dibutyryl adenosine 3':5'-cyclic monophosphate (db cyclic AMP) and db cyclic GMP. 7. An inhibitor of Na+,K(+)-ATPase, ouabain, 5 x 10(-5) mol l-1, prevented or reversed the depression of m.e.p.p. frequency by CCh. However, the depression was present in a nominally K(+)-free medium. Insulin and adrenaline, which are considered to be Na+,K(+)-ATPase activators, were without effect on depression of m.e.p.p. frequency. 8. The depression of m.e.p.p. frequency by 5 x 10(-6) M CCh was the same at temperatures between 5 and 30 degrees C with a Q10 near to 1.0. When threshold amounts of CCh were used (6 x 10-7 and 3 x 10-7 M), the depression was less at higher temperatures.9. The receptive structures responsible for the CCh (or ACh)-evoked depression of m.e.p.p. frequency differ pharmacologically from muscarinic, nicotinic ganglionic and neuromuscular junction ACh-receptors as well as from the synaptic cholinesterase, in contrast to previous reports (Duncan & Publicover, 1979).The low temperature-dependence points to the possibility that physical rather than biochemical processes are limiting in this presynaptic effect of cholinomimetics.

Acetylcholine↗
PubMed1990

Immobilization atrophy and membrane properties in rat skeletal muscle fibres.

Wet mass, resting membrane potential, frequency of miniature end-plate potentials and the concentration of [3H]ouabain-binding sites were studied after 7 days' immobilization of the rat soleus and extensor digitorum longus (EDL) muscles in the shortened or stretched position and after 3 and 7 days of remobilization. We observed that the loss of muscle mass by 37% in the rat soleus immobilized for 7 days in the shortened position is accompanied by a membrane depolarization of about 5 mV, a decrease in frequency of miniature end-plate potentials by 60% and a decrease of [3H]ouabain binding by 25%. Only minor changes were found in stretched soleus and in shortened and stretched EDL. After 3 days of remobilization of stretched soleus the muscle mass, [3H]ouabain binding and miniature end-plate potential frequency recovered to control values but the resting membrane potential continued to decrease. All changes induced by immobilization disappeared on day 7 of remobilization.

Animals↗