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A L Zefirov

Publications and source records attributed to A L Zefirov.

86 records · Page 5Linked to original sources
PubMed1976

[The functional heterogeneity of the synapses of the frog sartorius muscle].

Three main types of neuro-muscular junctions were revealed by means of the e.p.p. quantum content and the e.p.p. dynamics during high-frequency stimulation. Heterogeneity of synaptic apparatus seems to be mainly due to different intensities of quantum release. Subctances facilitating neuro-muscular transmission (Ca2+ ions, imidazol) were more effective in myoneural junctions with low e.p.p. quantum content, while depressing chemical agents (acetylcholine, tubocurarine) exerted a more potent effect in junctions with high quantum content.

Acetylcholine↗
PubMedDate not supplied

The effects of sodium nitroprusside on mediator release and the functional properties of postsynaptic membranes in the neuromuscular synapse.

Experiments on neuromuscular preparations of frog skin- thoracic muscle and sartorius muscle, using extracellular recording and two-electrode clamping of the muscle fiber membrane potential, were used to study the effects of the nitric oxide donor sodium nitroprusside on endplate currents. At a concentration of 100 microM, sodium nitroprusside sharply decreased the amplitude and quantum composition of the endplate currents, and also decreased the miniature endplate current frequency. The amplitude-time characteristics of miniature endplate currents, the voltage-dependent amplitude, and the decay time constant of miniature endplate currents did not change as compared with controls. However, unlike the situation with other secretion inhibitors, the decrease in endplate current amplitude was not accompanied by increased facilitation in response to rhythmic stimulation or changes in postsynaptic potentiation in conditions of application of pairs of stimuli to muscles. The suppression of acetylcholine secretion was not seen with inactivated sodium nitroprusside solution. These results provide evidence that nitric oxide can be a powerful inhibitor of both spontaneous and evoked transmitter secretion in the neuromuscular synapse, and that this is accompanied by decreases in the efficiency of presynaptic forms of short-term plasticity, while the functional characteristics of the postsynaptic membrane remain unchanged.

Action Potentials↗
PubMedDate not supplied

The effects of exogenous nitric oxide on the function of neuromuscular synapses.

Extracellular recording experiments using neuromuscular skin/chest muscle preparations from lake frogs were performed at low extracellular Ca2+ ion concentrations to study the effect of L-arginine (the substrate for nitric oxide synthesis) and N(G)-nitro-L-arginine methyl ester (a blocker of NO synthase) on the parameters of evoked transmitter secretion and ion currents in motor nerve endings. L-arginine at a concentration of 100 microM decreased the amplitude of endplate currents as well as their quantum composition, and also increased the amplitude of the third phase of the evoked nerve ending response, which reflects the kinetics of potassium influx currents. N(G)-nitro-L-arginine methyl ester at a condition of 100 microM led to increases in the amplitude and quantum composition of endplate currents and decreased the amplitude of the third phase of the evoked nerve ending response. It is suggested that endogenous nitric oxide is produced in frog neuromuscular synapses, which in normal conditions suppresses transmitter secretion and modulates the function of potassium channels in the nerve ending.

Animals↗
PubMedDate not supplied

[The physiological role of nitric oxide].

The review is devoted to exposition of a physiological role of a nitric oxide (NO), free radical gas, in various physiological functions. The number of those NO involvements is extremely high: bacteriocidal, cytotoxic and antitumor leukocyte effects, a relaxation of smooth-muscle cells of both vessels and gastrointestinal tract, the name just a few. The scheme of NO formation in various biological systems and its targets were shown and neuromodulator functions of NO in a brain were analyzed by the review presented. The findings of own researches on a role of NO in function of neuro-muscular synapse were included by the authors.

Animals↗
PubMedDate not supplied

[Changes in the asynchronism of transmitter release in a neuromuscular synapse and the time course of evoke postsynaptic signals during growth and branching og frog nerve ending].

The influence of both growth and branching of a nerve terminal on the asynchronism of transmitter release and the time-course of evoked postsynaptic responses was investigated using a model of a frog neuromuscular synapse in which the nerve terminal represents a population of spatially isolated active zones. It was shown that the appearance of additional branching in proximal parts of the nerve ending leads to decrease in the asynchronism of transmitter release, an increase in quantum content and the amplitude of the postsynaptic signal, and the shortening of its phase of growth. It was found that the asynchronism of transmitter release has a much stronger influence on the time-course of end plate currents compared with end plate potentials. The factors strengthening and weakening the asynchronism of transmitter release in a neuromuscular synapse and the reasons for various length and branching of vertebrate nerve terminals are considered.

Animals↗
PubMedDate not supplied

[The molecular mechanisms of quantum mediator secretion in the synapse].

The modern condition of knowledge about the molecular mechanisms underlying the quantal transmitter release in the central and the peripheric synapses is analysed. The data about the synaptic vesicles types, their forming, transporting to the sites of release at the nerve endings, exo- and endocytosis processes are presented. Ultrastructural and molecular organization of active zone of nerve ending and transmitter release morphofunctional unit--secretosome, which includes synaptic vesicle, exocytosis protein complex and calcium channels, are described. The basic proteins involved in the exo- and endocytosis and their interactions during transmitter release are examined. The role of the intracellular buffer systems, calcium micro- and macrodomains in the quantal transmitter secretion are considered. The reasons of the active zones functional non-uniformity and plasticity and factors reduced transmitter release in the active zone to the single quantum are analysed.

Animals↗
PubMedDate not supplied

[Ion channels in nerve ending].

The modern data about the structure and function of the nerve ending ion channels are generalized and systematized. Ion channels of nerve endings provide the forming of the rest membrane potential, excitability, generation of action potential, regulate the intracellular concentration of calcium ions, take part in exocytosis of synaptic vesicules, participate in short-term and long-term synaptic plasticity, ensure the modulation of presynaptic functions. Methods of investigation of ion channels and data about their localization in central and peripheral nerve systems are represented. The review gives the functional characteristics, molecular structure and mechanisms of regulation of the known voltage- and ligand-dependent ion channels, the role of the certain types of ion channels in the machinery of transmitter release.

Animals↗
PubMedDate not supplied

[Effect of chromium ions on the function of neuromuscular junctions].

It has been shown on neuro-muscular preparations of frog sartorius muscle that chromium ions in the concentrations 1-4 x 10(-6) g/ml strengthen spontaneous and evoked transmitter release. Cr3+ ions in the concentrations above 4 x 10(-6) g/ml decrease the membrane potential of muscle fibres, decrease the quantum content of the end plate potentials. Experiments on a single Ranvier node have shown that Cr3+ ions decrease the amplitude, increase the rate and duration of the action potential of a nerve fibre. It is concluded that chromium ions produce a pronounced effect on synaptic transmission, which differs significantly from the action of manganese, cobalt and nickel ions.

Action Potentials↗
PubMedDate not supplied

[Kinetics of nerve ending ion currents with nonhomogeneous distribution of ion channel density].

The Hodgkin-Huxley's equations of unmyelinated nerve fiber's electric behaviour has been used to create model of nerve endings electrogenesis. The Eler's integration method has been applied to solve the partial differential equation system which describes the spread of excitation in nerve ending. The effect of nonhomogeneous distribution densities of ionic channels along nerve ending on the ionic currents were simulated. The comparison of computed curves with nerve ending responses recorded by extracellular electrodes was performed. It was shown that the better match between simulated and recorded responses observes during densities' decrease potential-dependent sodium, potassium and calcium-activated potassium channels according to exponent along the nerve ending without changes of calcium channels density. As the result the amplitude and time-course of spread action potential, calcium current and transmitter release along the nerve ending appear to be changed.

Action Potentials↗
PubMedDate not supplied

[GABA--the basic mediator of excitation in the early stages of hippocampal development].

GABA is the principal neurotransmitter of inhibition in the adult mammalian brain. However, at early stages of development, including embryonic period and first week of postnatal life, GABA plays the role of main neurotransmitter of excitation. The paradoxical excitatory effect of GABA is due to an inversed chloride gradient and therefore a depolarizing direction of GABA-A receptor mediated responses. In addition, another type of GABAergic inhibition mediated by postsynaptic GABA-B receptors is not functional at early stage of life. In the neonatal rat hippocampus, GABA, acting via GABA-A receptors, activates voltage gated sodium and calcium channels and potentiates the activity of NMDA receptors by reducing their voltage dependent Mg2+ block. The temporal window when GABA exerts excitatory actions coincides with a particular pattern of activity of hippocampal neuronal network that is characterized by periodical giant depolarizing potentials (GDPs) reminiscent of interictal-like epileptiform discharges. Recent studies have shown that GDPs result from the synchronous discharge of GABAergic interneurons and principal glutamatergic pyramidal cells and are mediated by the synergistic excitatory actions of GABA-A and glutamate receptors. GDPs provide synchronous intracellular Ca2+ oscillations and may therefore be implicated in hebbian modulation of developing synapses and activity-dependent formation of the hippocampal network.

Aging↗