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Biomedical subjects

I A Shabunova

Publications and source records attributed to I A Shabunova.

At least 19 recordsLinked to original sources
PubMed1988

[Effect of a brain extract containing the postural asymmetry factor on the frog neuromuscular synapse].

The influence of the rat brain extract containing a postural asymmetry factor on the synaptic transmission in the right and left preparations of the frog cutaneus-pectoralis muscle was studied. The extract (2.10(-4) mg/ml) increased the quantal content of end-plate potentials (e.p.p.) in synapses of the right muscle and decreased it in synapses of the left muscle. In both right and left muscles relative changes in quantal content of e.p.p. correlated with relative changes in binomial parameter n. The results indicate an asymmetrical influence of the extract containing a postural asymmetry factor on the transmitter release in synapses of the right and left muscles.

Animals↗
PubMed1988

[Reactivating and cholinolytic action of dipyroxime in the myoneural synapse of warm-blooded animals].

Reactivating (RA) and cholinolytic (Chl) effects of dipyroxime in soleus and diaphragm muscles of the rat were estimated by amplitudes and durations of miniature end-plate potentials (MEPP) and currents (MEPC). After armin-induced inhibition of acetylcholinesterase (AchE), the action of dipyroxime in concentrations of 5.10(-6)-5.10(-4) mol/l on the amplitude and duration of MEPPs and MEPCs represents the combination of RA and Chl effects. Separate study of the RA effect (after washing out of the reactivator) has shown that this effect increased within the whole range of concentrations used. Complete reactivation of phosphorylated AchE was achieved at dipyroxime concentrations of 2-5.10(-4) mol/l. Separate analysis of Chl effect (in voltage-clamp experiments with intact AchE) has shown that dipyroxime suppressed acetylcholine-induced responses due to a block of cholinoreceptors in the open conformation. This block was characterized by prolongation of MEPCs decay without affecting its exponential nature. It is concluded that dipyroxime is a "very fast blocker".

Acetylcholinesterase↗
PubMed1987

[Dipyroxime as a blocker of ion channels activated by acetylcholine in rat skeletal muscle].

The mechanism of cholinolytic action of dipyroxime--reactivator of the phosphorylated acetylcholinesterase were investigated in the rat diaphragm muscle by voltage-clamp technique. Dipyroxime reduced the amplitude and prolonged the decay of the miniature end-plate currents (MEPC) without affecting its exponential nature. Current-voltage relationship exhibited negative conduction in the hyperpolarized region. Dipyroxime increased the voltage dependence of the time constant of MEPC decay (the membrane potential alteration necessary for e-fold change of the decay time constant reduced from 80 to 35 mV). It was concluded that dipyroxime is a very fast blocker of the open end-plate channels.

Acetylcholine↗
PubMed1986

[Release of beta-alanine from the frog skeletal muscle determined by thin-layer chromatography].

The release of beta-alanine from the resting and contracting frog sartorius muscles was demonstrated by the two-dimensional thin-layer chromatography. The release of beta-alanine from indirectly stimulated muscles of frogs in winter was about 230% higher than at rest. When synaptic transmission was blocked by d-tubocurarine the release of beta-alanine from directly stimulated muscles did not exceed the release at rest. Thus, activation of neuromuscular synapse leads to increased beta-alanine release from contracting muscle.

Alanine↗
PubMed1984

Reversal potential of the end-plate currents and potassium feedback at the neuromuscular synapse.

The experiments were carried out at the neuromuscular junction of the frog. Erev of epc was estimated by two methods--extrapolation and interpolation. In K+-enriched solution Erev obtained by linear extrapolation from high-mp region changed according to the Takeuchi equation. The behavior of Erev obtained by interpolation was better described by the Goldman-Hodgkin-Katz equation. Under the change of the nerve stimulation frequency from 0.5 to 50/sec, the positive shift of Erev estimated by both methods was observed. This indicates K+ accumulation in active synaptic segments during activity. The elimination of the potassium current of epc by clamping of mp at the - 130 mV level resulted in the lowering of facilitation under paired nerve stimulation (20 msec interval) and in the decrease of the rate of facilitation under 50/sec frequency stimulation. The data support the presence of antidromic K+ action in the neuromuscular synapse.

Animals↗
PubMed1984

[Effect of long-term postsynaptic membrane voltage clamp at different levels on neuromuscular transmission in the frog].

The effects of the polarizing current on the neuromuscular transmission in frogs were estimated with the voltage-clamp technique. The spontaneous and evoked transmitter release was unchanged in the muscle membrane potential ranging from -130 to -60 mV. The quantum content of the transmission decreased by 35-40% at the -40 mV membrane potential level, the increase in the miniature e. p. p. frequency being insignificant. The values of the reversal potentials estimated by interpolation were the same for the two initial levels (-80 and -40 mV) of the clamped membrane potential. The muscle fiber membrane depolarization seems to cause the potassium accumulation in the muscle extracellular space mainly near the current microelectrode. The accumulation in the synaptic cleft is less obvious, hence the latter may be regarded as a compartment of the intracellular space with the relatively independent ionic content.

Animals↗
PubMed1984

[Antidromic action of potassium in the neuromotor synapse].

The possibility of potassium accumulation in the synaptic cleft and a participation of its antidromic action in the regulation of presynaptic processes were estimated in experiments on neuromuscular junctions of the frog. In potassium-enriched solution, the reversal potential obtained by the linear extrapolation from the region of high membrane potentials was considerably altered according to the Takeuchi equation. The change of the reversal potential obtained by interpolation was insignificant as predicted by the Goldman--Hodgkin--Katz equation. In normal solution under the change of the nerve stimulation frequency from 0.5/sec to 50/sec the positive shift of the reversal potential occurred as revealed by both techniques. This indicates potassium accumulation in active synaptic segments during the activity. Elimination of the potassium component in the end-plate current by clamping of the membrane potential at the -130 mV level resulted in lowering of facilitation under paired nerve stimulation (20 msec interval) and in a decrease of the facilitation rate under 50/sec stimulation. The data corroborate an antidromic potassium action on the neuromuscular synapse.

Animals↗
PubMed1982

[Effect of cholinesterase inhibitors on the electrical excitability of the membrane of frog muscle fiber].

The effects of reversible (galanthamine, eserine) and irreversible organophosphate (armine) cholinesterase inhibitors on excitable muscle fibre membrane of the frog involved elongation of the rise and the half-decay time of the AP (galanthamine and eserine), the critical level of depolarization being shifted to a more negative value. Armine decreased the rise and the half-decay time, the critical level of depolarization being shifted to the positive direction; subsequent rising of the threshold often caused blocking of neuro-muscular transmission during the first minutes of the armine action, pretreatment of preparations with galanthamine (eserine) preventing the threshold increase and armine blocking of transmission. Probably mechanism of these drugs action on the membrane channels is discussed. The negative shift of critical level seems to underlie the protective action of galanthamine and eserine in case of poisoning with irreversible cholinesterase inhibitors.

Action Potentials↗
PubMed1981

[Effect of armin on synaptic transmission in frog neuromuscular preparations].

The action of armin, an organophosphorus inhibitor of cholinesterases, on synaptic transmission parameters was studied by means of intracellular registration of end plate potentials and currents (EPP and EPC) in the frog. On 10-minute exposure the increase in the temporary parameters became manifest provided the drug was administered at a concentration of 10(-6) g/ml and over. EPC reversal potential and cholinoreceptor sensitivity to armin did not change substantially. At a concentration of 10-(-8) g/ml armin exerted a potentiating effect on the frequency of miniature EPP and quantum composition of EPP, while that effect was not related to armin anticholinesterase activity. The presynaptic acetylcholine release was suppressed by high concentration of armin (10(-5) g/ml). Under the conditions cited there was a decrease in the depot of the available transmitter quanta in nerve terminals.

Acetylcholine↗
PubMed1978

On potassium functional feedback in neuromuscular junction.

The dependence of the reversal potential (Erev) of intracellular end-plate potentials (epp) on activity patterns was studied in frog neuromuscular preparations. A shift of Erev to the positive side was found with change in frequency of stimulation from 1/sec to 50/sec. This shift corresponds to the increase of potassium concentration in the synaptic cleft to 7.0 mM. The effect of potassium concentration [K+]0 in the bath solution on quantal content (m) of epp was studied. The quantity m increased when [K+]0 was varied within the range 4.7-8.7 mM; m decreased when [K+]0 was greater than 8.7 mM. Such a relationship between m and [K+]0 is accounted for by the combined effect of potassium on transmitter secretion and electrogenic processes in motor nerve terminals. The correlation between the change of m with [K+]0 and initial epp amplitudes was found and was attributed to potassium efflux from post-synaptic region in varying quantity depending on the initial epp amplitudes. A scheme of synaptic self-regulation by means of potassium feedback is suggested.

Animals↗
PubMed1977

[Pre-synaptic effect of histidine at neuromuscular junctions].

The influence of L-histidine in different concentrations (0.2--9.0mM) on synaptic processes in neuro-muscular preparations of the frog was studied using intracellular microelectrodes. The histidine caused lowering of the frequency of m. e. p. p. In the synapses with initial quantum content of e. p. p. less than 50, the increase of quantum content occurred due to rising of the available mediator level. The possibility of the transmitter release did not change. The histidine seems to participate in positive functional feedback in a neuro-muscular synapse, the feedback maybe essential for mobilization of the inactive synapses during intense muscular activity.

Animals↗