Biomedical subjects

F Vyskocil

Publications and source records attributed to F Vyskocil.

At least 37 records · Page 2Linked to original sources

PubMed2000

[Intracellular cAMP involvement in the synchronized activity of noradrenaline in response to evoked release of the transmitter quanta in the frog synapses].

An analogue of cyclic AMP (db-cAMP) penetrating into the frog neuromuscular junction's cell, as well as the adenylyl cyclase activator forskolin, and inhibitor of nucleotide-depending phosphodiesterase isobutilmethylxantine alter the kinetics of the quanta secretion resulting in synchronizing of the process of the transmitter release. Following a db-cAMP preliminary action, no such synchronizing of the transmitter release occurred. Action of noradrenaline on the time course of the secretion seems to be realised through activation of presynaptic beta-adrenoreceptors, augmentation of the adenylyl cyclase activity, and the rise of the intracellular cAMP.

1-Methyl-3-isobutylxanthine↗

PubMed2000

Cyclic AMP synchronizes evoked quantal release at frog neuromuscular junctions.

At frog neuromuscular junction, noradrenaline (NA) shortens the release period for evoked quantal release acting on a beta1 receptor. To test the hypothesis that this action of NA is mediated by cAMP, we measured the latencies of focally recorded uni-quantal endplate currents (EPCs) after application of dibutyryl-cAMP (db-cAMP) and adenylyl cyclase activator, forskolin. The interval between the time when responses with minimal delay appeared and the point at which 90% of all latencies had occurred (P90 parameter) was shortened in the presence of both 1 x 10(-6) mol/l db-cAMP and 1 x 10(-6) mol/l forskolin by about 30%. The cAMP-induced shortening is equal to that found after application of NA and effects of both drugs are not additive.

Acetylcholine↗

PubMed2000

Participation of electrogenic Na+-K+-ATPase in the membrane potential of earthworm body wall muscles.

The effect of Na+-K+-ATPase inhibitor ouabain on the resting membrane potential (Vm) was studied by glass microelectrodes in isolated somatic longitudinal muscles of the earthworm Lumbricus terrestris and compared with frog sartorius muscle. In earthworm muscle, Vm was -49 mV (inside negative) in a reference external solution with 4 mmol/l K+. The electrogenic participation of Na+-K+-ATPase was absent in solutions with very low concentrations of 0.01 mmol/l K+, higher in 4 and 8 mmol/l K+ (4-5 mV) and maximal (13 mV) in solutions containing 12 mmol/l K+ where Vm was -46 mV in the absence and -33 mV in the presence of 1 x 10(4) M ouabain. The electrogenic participation of Na+-K+-ATPase was much smaller in m. sartorius of the frog Rana temporaria bathed in 8 and 12 mmol/l K+. The results indicate that the Na+-K+-ATPase is an important electrogenic factor in earthworm longitudinal muscle fibres and that its contribution to Vm depends directly on the concentration of K+ in the bathing solution.

Animals↗

PubMed2000

[Pre- and postsynaptic effects of the calcium channel blocker verapamil in the nerve-muscle preparation].

Verapamil did not change the amplitude of the miniature and multiquantal end-plate currents, synchronicity of the transmitter release and repetitive firing at the motor nerve endings. Verapamil shortened the decay of multiquantal currents, the effect being enhanced after acetylcholinesterase inhibition. In muscles with inhibited acetylcholinesterase, verapamil promoted the depression of successive end-late currents in rhythmic nerve stimulation. The data suggest that in skeletal muscles verapamil-sensitive calcium channels do not take part in physiological transmitter release or in chemical potentiation of the secretion after treatment with potassium channels blocking agents.

Acetylcholinesterase↗

PubMed1999

Noradrenaline synchronizes evoked quantal release at frog neuromuscular junctions.

1. Noradrenaline (NA) increases synaptic efficacy at the frog neuromuscular junction. To test the hypothesis that one of the actions of NA is to shorten the period over which evoked quanta are released, we measured the latencies of focally recorded uniquantal endplate currents (EPCs). 2. NA shortened the release period for evoked quantal release. The interval between the time when responses with minimal delay appeared and the point at which 90 % of all latencies had occurred was shortened in the presence of 1 x 10-5 M NA by about 35 % at 20 C and by about 45 % at 8 C. Inhibitor and agonist experiments showed that NA acts on a beta-adrenoreceptor. 3. The better synchronization of release significantly increased the size of reconstructed multi- quantal EPCs. This suggests that NA facilitates synaptic transmission by making the release of quanta more synchronous. 4. The synchronizing action of NA might potentiate neuromuscular transmission during nerve regeneration, transmitter exhaustion and other extreme physiological states where the quantal content is reduced, such as survival in cold and hibernation.

Adrenergic alpha-Agonists↗

PubMed1999

The glutamate and carbachol effects on the early post-denervation depolarization in rat diaphragm are directed towards furosemide-sensitive chloride transport.

The membrane potentials of denervated muscle fibres of the rat diaphragm kept in a tissue culture medium are depolarized by about 8-10 mV (10-12%) within 3 h after denervation. This early post-denervation depolarization (EPD) is substantially reduced (2-3 mV) when muscle strips are bathed with 1 mM L-glutamate (GLU) which is found in motor nerve endings, or with 5 x 10(-8) M carbachol (CCh), which mimics the effect of nonquantally released acetylcholine (ACh). The hyperpolarizing effects of GLU and CCh on EPD are not influenced by ouabain, an active sodium transport inhibitor, but are absent when Cl- transport is augmented by increased osmolarity (500 mosmol/l) produced by addition of sucrose or NaCl. The EPD and the effect of hyperosmolarity are effectively prevented by the Cl- transport inhibitor furosemide (1 x 10(-4) M) or by a chloride-free bathing medium. It is suggested that the post-denervation cessation of nonquantal ACh release, and probably also GLU release, from nerve endings leads to the activation of the furosemide-sensitive Cl- transport in the sarcolemma, which is responsible for the early post-denervation depolarization.

Animals↗

PubMed1999

Non-quantal acetylcholine release is increased after nitric oxide synthase inhibition.

After anticholinesterase treatment, depolarization of the postsynaptic muscle membrane by about 5 mV develops due to non-quantally released acetylcholine from the motor nerve terminal and can be revealed as hyperpolarization by the addition of curare (H-effect). The H-effect increases significantly to 8.7 mV after inhibition of NO-synthase by L-nitroarginine methylester (L-NAME) whilst no changes in the amplitude and frequency of quantal miniature endplate potentials are observed.

Acetylcholine↗

PubMed1998

The effect of glutamate and inhibitors of NMDA receptors on postdenervation decrease of membrane potential in rat diaphragm.

The early postdenervation depolarization of rat diaphragm muscle fibers (8-10 mV within 3 h in vitro) is substantially smaller (3 mV) when muscles are bathed with 1 x 10(-3) M L-glutamate (Glu) or 1 x 10(-3) M N-methyl-D-aspartate (NMDA). The effects of Glu and NMDA are inhibited in a dose-dependent manner by competitive inhibitor 2-amino-5-phosphonovaleric acid (APV) with Ki 6.3 x 10(-4) M, by 2 x 10(-7) M MK-801, which acts as an open channel inhibitor, by 2-3 x 10(-4) Zn2+, which reacts with surface-located sites of the NMDA subtype of the glutamate receptor, and also by glycine-free solutions and 7-Cl-kynurenic acid, which inhibits the glycine binding sites on NMDA receptors. It follows that the effect of glutamate on early post-denervation depolarization is mediated by the NMDA subtype of glutamate receptor with similar pharmacological properties to those found in neurons. The only exception found was the glutamate-like action of 1 x 10(-7) M MK-801, which partially prevented the early postdenervation depolarization when present in the muscle bath during the first 3 h after nerve section.

Animals↗

PubMed1998

[Synchronization of secretion of the evoked transmitter quanta as mechanism of the facilitating action of sympathomimetics].

Noradrenaline, isoproterenol, dobutamine were found to modulate kinetics of quanta secretion so as to synchronize the transmitter release. This effect could be prevented with blocking agents of beta-adrenoreceptor (atenolol, propranolol). Activators of beta-adrenoreceptors klonidine and phenylephrine did not change the kinetics of quanta secretion, whereas phentolamine did not affect the synchronizing effect of noradrenaline. The change in the time course of the secretion induced by noradrenaline increased the end-plate current amplitude. There seems to exist a specific presynaptic mechanism involving beta-adrenoreceptors for facilitation of effects of sympathomimetics.

Action Potentials↗

PubMed1998

Carnosine and other imidazole-containing compounds enhance the postdenervation depolarization of the rat diaphragm fibres.

In the presence of carnosine, anserine, histidine, imidazole and 7-nitro indazole, the early postdenervation depolarization of muscle of about 8 mV was significantly increased by 2.15-4.8 mV. The presence of the imidazole ring in the molecule is apparently necessary for this effect. These compounds also eliminated an NO-mediated protective effect of L-glutamate and carbachol on the depolarization of membrane potential. The presence of imidazole, 7-nitro indazole, carnosine and anserine did not significantly change the effect of an external NO donor, sodium nitroprusside. The structural and functional similarity between imidazole derivatives and the known NO synthase inhibitor, 7-nitro indazole suggests that imidazole, carnosine and anserine might act by inhibiting NO production which is stimulated by glutamate and carbachol.

Animals↗

PubMed1998

Ca(2+)-induced inhibition of sodium pump: effects on energetic metabolism of mouse diaphragm tissue.

Tissues of mouse diaphragms were incubated in Liley solution containing 2, 4, 6 and 10 mmol/l calcium. When diaphragm tissue was incubated in 10 mmol/l calcium, an increase of intracellular calcium concentration from 314 +/- 28 to 637 +/- 26 nmol/l was estimated by fluorescent Ca2+ indicator Fura-2/AM. Moreover, incubation of the tissue in 10 mmol/l Ca2+ led to complete inhibition of electrogenic activity of the sodium pump, as measured by intracellular microelectrodes in a single muscle cell. This inhibition was fully reversible after 5 min washing with Liley solution containing 2 mmol/l CaCl2. The Ca(2+)-induced blocking effect on electrogenic activity of the sodium pump was accompanied by inhibition of glucose incorporation into the muscle tissue. Calcium at concentrations of 6 and 10 mmol/l in bath medium significantly inhibited both CO2 production and O2 consumption. A continual decrease of respiration (CO2/O2) quotient was observed under increasing concentrations of calcium. Moreover, an exponential decrease of ATP tissue levels was observed at increasing concentrations of calcium in the bath medium. On the other hand, massive acceleration of anaerobic glycolysis induced by incubation of the tissue in a medium containing high calcium concentration is improbable. This may be deduced from the fact that only about an 50% increase of lactate content in muscle tissue was observed when diaphragms were incubated for 30 min in medium containing calcium ions at 6 and 10 mmol/l as compared with the control tissue incubated for the same time in the medium containing 2 mmol/l CaCl2. In conclusion it could be stressed that increase of Ca2+ concentration in bath medium induced in diaphragm muscle tissue an elevation of intracellular Ca2+ concentration accompanied by a depression of sodium pump electrogenic activity and a depression of energy metabolism. These changes may be involved in pathology of muscle tissue during the Ca2+ overload.

Animals↗

PubMed1997

Desensitization shortens the high-quantal-content endplate current time course in frog muscle with intact cholinesterase.

1. The desensitization induced by bath-applied carbachol or acetylcholine (ACh) and potentiated by proadifen (SKF 525A) was studied in the frog sartorius with intact synaptic acetylcholinesterase (AChE). 2. The reduction in the density and number of postsynaptic receptors produced by desensitization lowered the amplitude of the endplate currents (EPCs) and shortened the EPC decay when the quantal content (m) of the EPC was about 170 and when multiple release of quanta at single active zones was highly probably. The shortening of high-quantal-content EPCs persisted for at least 15 min after the wash-out of agonists, at a time when the amplitude had recovered fully. 3. The decay times of the low-quantal-content EPCs recorded from preparations pretreated with 5 mM Mg2+ (m approximately 70) and single-quantum miniature endplate currents (MEPCs) were not affected by carbachol, ACh or proadifen. 4. The desensitization of ACh receptors potentiated by proadifen, prevented completely the 6- to 8-fold prolongation of EPC which was induced by neostigmine inhibition of synaptic AChE. 5. It is assumed that high-quantal-content EPCs increase the incidence of multiple quanta release at single active zones and the probability of repetitive binding of ACh molecules which leads to EPC prolongation. The shortening which persists after complete recovery of the amplitude during wash-out of the exogenous agonist is probably due to 'trapping' of ACh molecules onto rapidly desensitized receptors and the reduced density of functional AChRs during the quantum action.

Acetylcholine↗

PubMed1997

Acetylcholine and carbachol prevent muscle depolarization in denervated rat diaphragm.

Muscle fibres of the rat diaphragm kept in a tissue culture medium became depolarized by 8-10 mV within 3 h after denervation. In the presence of carbachol (CB; 5 x 10(-8) M), and acetylcholine (ACh; 5 x 10(-8) M, the post-denervation depolarization was reduced. Both drugs were used in concentrations which mimicked the effect of non-quantal release of ACh. (+)Tubocurarine (TC) and ouabain did not prevent the protective action of CB, indicating that this effect is not mediated through ACh nicotinic receptors or the electrogenic Na+, K+ pump. Addition of Mg2+, verapamil, diltiazem, nifedipine and Cd2+ in concentrations which block Ca2+ entry virtually inhibited the effect of both cholinomimetics. L-Nitroarginine methylester (NAME), an inhibitor of NO synthase, and haemoglobin, an extracellular scavenger of the NO radical, completely eliminated the protective effect of CB on post-denervation depolarization. The retrograde action of NO produced by cholinomimetics on nerve terminals is postulated.

Acetylcholine↗

PubMed1996

Nitroprusside decreases the early post-denervation depolarization of diaphragm muscle fibres of the rat.

The application of sodium nitroprusside, which degrades to nitric oxide (NO) in solution, inhibits early post-denervation depolarization of isolated rat diaphragm fibres. The observation that "old' solutions of sodium nitroprusside (that have been allowed to decompose) are without effect and that haemoglobin, oxadiazolo quinoxalinone (ODQ) and methylene blue can antagonize the inhibition normally produced by sodium nitroprusside suggests that the inhibitory effects of sodium nitroprusside on early post-denervation depolarization are mediated by NO and guanylyl cyclase. This is in accord with our recent observations with NO synthase activation and inhibition in the diaphragm.

Animals↗

PubMed1996

Non-quantal acetylcholine release in the mouse diaphragm after phrenic nerve crush and during recovery.

The progressive decline and recovery of spontaneous quantal acetylcholine (ACh) release (miniature endplate potentials, MEPPs) and the H-effect were measured in the mouse diaphragm after nerve crush and during regeneration. The H-effect is the hyperpolarization of the muscle fibre membrane produced by the addition of (+)tubocurarine, which indicates non-quantal ACh release. One hour after nerve crush the H-effect had declined to 50% of control values and 4 h later the H-effect disappeared completely. There were no substantial changes in the MEPP frequency and amplitude during the first 4 h after denervation. MEPP frequency then increased, but after 6 h of denervation it decreased and after 16 h no MEPPs were found in any of the muscle fibres. The times of onset of these denervation changes in the proximal, central and distal parts of diaphragm were similar. During reinnervation, the H-effect was detectable in all muscle parts 3 days before the reappearance of MEPPs. The H-effect developed first on day 8 in the proximal endplates and then, with a delay of 3 and 6 days, in the central and distal areas, respectively. During axonal regrowth the non-quantal release was restored before detectable quantal release. Non-quantal release is the first indication of the ability of the nerve terminal to release ACh in the process of reinnervation.

Acetylcholine↗

PubMed1995

7-Oxo-prostacyclin affects the electrogenic Na+/K+ pump in mouse diaphragm fibers.

The effect of a stable prostacyclin derivative, 7-oxo-prostacyclin, on the electrogenic Na+/K+ pump in mouse diaphragm muscle was investigated. Resting membrane potentials of muscle cells were measured with glass microelectrodes. In fresh diaphragm preparations from 7-oxo-prostacyclin-pretreated mice (50 micrograms.kg-1 7-oxo-prostacyclin i.p. 30-34 h prior to the experiment) resting membrane potentials were significantly higher (-83.86 +/- 1.40 mV, mean +/- S.E.M.) than in control preparations (-70.78 +/- 1.07 mV). Ouabain at a concentration of 10(-4) mol.l-1 abolished this hyperpolarization (P < 0.05). The electrogenic effect induced by addition of 5 mmol.l-1 K+ to Na(+)-loaded muscles from 7-oxo-prostacyclin-pretreated animals was also enhanced (delta resting membrane potential = 21.73 +/- 3.13 mV) compared with that of the controls (delta resting membrane potential = 18.36 +/- 1.29 mV). Ouabain antagonized the increase in electrogenicity of Na(+)-loaded diaphragms induced by 7-oxo-prostacyclin pretreatment (P < 0.05). In contrast to control preparations, no inhibition of the electrogenic effect induced by 10 mmol.l-1 Ca2+ ions in Na(+)-loaded muscles was observed in diaphragms from 7-oxo-prostacyclin-pretreated animals. In acute experiments with Na(+)-loaded muscles, where 10(-7) mol.l-1 7-oxo-prostacyclin was added to the bath, resting membrane potential reached up to -100 mV. The electrogenic pump-induced increase in resting membrane potential amounted to approximately 30 mV. This effect could be also abolished by 10(-4) mol.l-1 ouabain (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Modelling endplate currents: dependence on quantum secretion probability and decay of miniature current.

Quantification of the time course and amplitude of endplate currents (EPC) was made with respect to dispersion of quanta secretion and to changes in the exponential decay of miniature endplate currents (tau mepc). The relationship between RPC amplitude and tau mepc follows a double-exponential curve with tau1 = 0.3 ms and tau2 = 6 ms. If the amplitude of fully synchronised EPC is taken as 100%, then the loss of EPC amplitude is already 42% with "physiological" parameters of dispersion (the half-rise and decay constant of distribution of secretion probability = 0.5 ms, taumepc = 1 ms). This loss is even more substantial if secretion is more dispersed or miniature endplate currents decay faster.

Acetylcholine↗

PubMed1995

The effects of calcium and calcium channel blockers on sodium pump.

The effects of 10 mM Ca2+ and Ca2+ channel blockers verapamil, diltiazem and flunarizine on the ouabain-sensitive electrogenic Na+, K+ pump activity of mouse diaphragm muscle fibres enriched with Na+ were compared with the changes in cytosolic [Ca2+]. The electrogenic Na+ pump activity produced by adding K+ to muscles previously bathed for 4 h in a K(+)-free, 2-mM [Ca2+] solution increased the resting membrane potential by about 18 mV. This hyperpolarization was completely inhibited after 10 min incubation in 10 mM Ca2+. Verapamil 10(-5) M, 10(-5) M diltiazem and 10(-7) M flunarizine effectively prevented the effect of elevated [Ca2+]. At these concentrations, these drugs did not affect the K(+)-induced hyperpolarization. In mouse diaphragm, the basal cytosolic [Ca2+] measured by the fluorescent indicator 1-[2-(5-carboxyoxazol-2-yl)-6- aminobenzofuran-5-oxy]2-(2'-amino-5'-methylphenoxy)ethane-N,N,N',N '- tetraacetic acid acetoxymethyl ester (fura-2/AM) was 261 +/- 6 nM. After 4 h in a Liley K(+)-free, 2 mM [Ca2+] solution, the cytosolic [Ca2+] increased to 314 +/- 28 nM. Increase in [Ca2+] from 2 to 10 mM caused a twofold increase of cytosolic [Ca2+] to 637 +/- 26 nM. This rise was, like the Ca(2+)-induced inhibition of electrogenic pump, prevented by 10(-5) M verapamil, 10(-5) M diltiazem and 10(-7) M flunarizine. The results suggest that substances which block Ca2+ entry into the cell prevent the Ca(2+)-induced inhibition of the Na+ pump.

Animals↗