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Biomedical subjects

A L Zefirov

Publications and source records attributed to A L Zefirov.

At least 73 records · Page 4Linked to original sources
PubMed1985

[Characteristics of electrical activity in different sections of nerve endings in the frog].

In experiments on frog sartorius neuromuscular preparations, the evoked electrical responses of nerve endings were recorded by extracellular microelectrodes. It was shown that in proximal parts of the nerve ending, the three-phase response (+ - +) with a high amplitude negative phase occurred due to motor nerve stimulation. With movement of the extracellular electrode in distal direction a certain increase of the initial positive phase and a significant decrease of the negative one were observed. At the end of the terminal that response transformed to the monophasic one (+). On local iontophoretic application of tetrodotoxin (TTX) to the recording site two components of the nerve ending response were revealed: TTX-insensitive and TTX-sensitive. A significant decrease of the TTX-sensitive component occurred along the course of the nerve ending. That component was absent from the distal synaptic areas. It is concluded that in frog nerve ending, the action potential propogates with decrement while depolarization of the end parts of the terminal is passive in nature.

Action Potentials↗
PubMed1984

[Analysis of factors limiting the applications of binomial statistics in studies of mediator secretion at neuromuscular synapses].

Binomial parameters of transmitter secretion were calculated on the basis of synaptic potential analyses at frog sartorius muscle. In some synapses negative values of parameter of the p were found. These negative values often occurred at low concentrations of Ca2+ ions and small amplitude of miniature end plate potentials. The obtained data were interpreted in terms of a model which presupposes the heterogeneity of the quantum transmitter release at different sites. A computer imitation of transmitter secretion showed that the appearance of the negative p parameter values and erroneous n estimations in the experiment are related with the shape of the distribution of quantum transmitter release probability and the amplitude of miniature end plate potentials.

Animals↗
PubMed1984

[Electrophysiological evaluation of mediator secretion and pool at an individual point of neuromuscular synapse release in the frog].

The time-course of one-quantum end plate potentials during repetitive stimulation of the motor nerve (5-10 imp/sec) was studied under iontophoretic application of Ca2+ to the nerve ending with the aid of high-resistance exocellular microelectrodes. It was found that long-term stimulation was first accompanied by rapid and then by a slower decrease of transmitter release. After 2 to 3 minutes of stimulation the level of secretion reached a plateau. Blockade of acetylcholine synthesis by hemicholinium-3 did not affect the time-course of transmitter secretion drop but led to the disappearance of the plateau state. Electrophysiological study of transmitter exchange in an individual point of release provided the following values: the available transmitter pool 32-47 quanta, the mobilization pool 120-320 quanta, the rate of transmitter synthesis 0.3-1.0 quanta/s.

Action Potentials↗
PubMed1984

[Electrophysiological and morphological study of the synaptic organization of the tonic muscle fibers in the frog].

The histochemical and electrophysiological investigation of tonic muscle fibers was performed in the frog m. cruralis. Cholinesterase activity studies in tonic fibers revealed 4 to 14 synapses aggregated in groups. A number of synapses were in positive correlation with the muscle fibers length. In MPSP recording, the distribution of amplitude, periods of growth and of half-time decay had a nonsymmetrical form. At the scatter diagrams of MPSP amplitude recorded by two intracellular microelectrodes, two to six signal groups were revealed in single synapses at different distances from the site of recording. The groups were represented by different number of signals of various duration. Similar groups of signals were also found in evoked PSP, the number of such groups depending upon the intensity of nerve stimulation. The synapses formed by a single motor axon seem to congregate in certain areas of tonic fibers and to be functionally heterogeneous. Intracellular recording revealed only a part of the tonic fibre synapses.

Animals↗
PubMed1983

[Multimodality in the amplitude distribution of miniature endplate potentials due to the action of spatially discrete areas of transmitter release].

Miniature end plate potentials (MEPPs) were simultaneously recorded in frog sartorius muscle by two intracellular microelectrodes. Some isolated groups of points (clouds) were found on the diagram of MEPPs scatter. Several peaks each of which was composed of signals from certain clouds (or from several clouds) on the scatter diagram were found on the histograms of MEPPs amplitude distribution. It is assumed that the clouds on the scatter histogram and the peaks on the histogram of MEPPs amplitudes are formed at the cost of secretion of quantum acetylcholine from spatial separate areas of transmitter release. The data obtained do not correspond with the subquantum hypothesis of transmitter release in neuromuscular junctions.

Animals↗
PubMed1983

[Mediator secretion in the proximal and distal portions of a nerve ending of the sartorius muscle in the frog].

In experiments on neuromuscular preparations of the frog sartorius muscle the evoked transmitter release was investigated by extracellular recording. A decrease of the evoked transmitter release from proximal to distal parts of nerve terminals was observed related to a decrease in probability of transmitter quantum release. The terminal part of synapse showed smaller sensitivity to an increase in extracellular Ca2+ concentration as compared with the proximal part, smaller facilitation of transmitter release at double and repetitive stimulation, deeper and more quickly developing depression. A conclusion is made that these peculiarities of the transmitter release in the terminal parts of the synapse are due to smaller transmitter reserve and smaller permeability of the presynaptic membrane to Ca2+ ions.

Animals↗
PubMed1983

[Analysis of polymodality in the distribution of latent periods and amplitudes of single-quantum synaptic potentials in the frog neuromuscular junction].

Intracellular recording with low concentrations of Ca2+ ions as analysed in the histograms of latency values and amplitude distributions, revealed 4-7 peaks in unitary potentials from the neuromuscular junction in the frog sartorius muscle. The increase of Ca2+ ions concentration led to disappearance of the multimodality. Extracellular recording revealed but a single mode in histograms of distributions. The number of modes in latency values distributions was found to have a positive correlation with values of the binominal parameter n and the number of peaks in histograms of the EP amplitudes. The peaks in histograms of distribution of the latency values and amplitudes of unitary EPs seem to reflect the action of transmitter release in the nerve terminals.

Action Potentials↗
PubMed1982

[Mechanism of facilitated transmitter release in the neuromuscular synapse].

In the frog m. sartorius preparation, the intracellular recording at large concentrations of Ca2+ ions revealed two components in the facilitation following a single stimulus applied to the motor nerve. A decrease in the [Ca0] concentration led to appearance of an additional very early component of the facilitation. Extracellular recording always revealed all three components. In rhythmical stimulation, the early facilitation component is summed up according to the power model of facilitation summation with the power index 2 to 5 depending on initial probability of a quantum transmitter release. The first and the second components are summed up according to the linear facilitation model.

Animals↗
PubMed1982

[Statistical analysis of calcium accumulation in nerve endings during rhythmic stimulation].

The extracellular recording was used to examine the evoked transmitter release in neuromuscular junctions of the frog sartorius muscle at pair and repetitive stimulations. The repetitive stimulation with low initial level of secretion (the quantum content 0.1-0.5) led to the increased transmitter release. Statistical analysis showed that the probability of the quantum transmitter release in response to each stimulus was increased. The method of conditioned probabilities revealed a decrease in the probability of the quantum release provided the previous stimulus had induced the secretion of the acetylcholine quantum. It is assumed that at the moment of the quantum transmitter release (or promptly after it) a certain quantity of Ca2+ leaves the nerve terminal cytoplasm, thereby significantly reducing the intracellular concentration of calcium.

Animals↗
PubMed1982

[Model of mediator secretion at a neuromuscular synapse based on the spatial heterogeneity of the probability of acetylcholine quantum release].

A spatial heterogeneity of the probability of the mediator quantum release (pt) along the nerve terminal was found in experiments on frog sartorius muscle with extracellular recording of end-plate potentials. The expression of Ca2+ ions effect depended upon the initial pt. With intracellular recording the increase of Ca2+ concentration from 0.2 to 1.8 mM was accompanied by increase of n and p binomial parameters. On the basis of the obtained data a model of mediator release at neuromuscular synapsis is proposed, which allows the estimation of the coefficients of pt distribution along the nerve terminal and the number of acting release sites. For estimation of these parameters it is necessary to calculate the n and p at two different Ca2+ ion concentrations.

Acetylcholine↗
PubMed1981

[Analysis of frequency facilitation in neuromuscular synapses of the sartorius muscle in frogs].

Changes in the quantum content of end plate potentials (EPPs) were studied in experiments on the frog sartorius muscle in the course of a gradual increase in stimulation frequency (frequency facilitation). It was shown that the frequency facilitation coefficient does not depend on the initial quantum content of EPPs but is in good agreement with the initial frequency of miniature EPPs and in bad agreement with their amplitude. The frequency facilitation is accompanied by the growth of the statistical binomial parameters P and n. The increase in P parameters is consequent of interference in P changes during the second component of facilitation after the single impulse. The growth of n is accounted for by the summation of the n increase during the first component of facilitation the time course of which is prolonged on repetitive stimulation.

Animals↗
PubMed1980

[Effect of calcium ions on bimodal parameters of mediator liberation in frog sartorius muscle neuromuscular junctions].

In synaptic junctions of the frog sartorius muscle, the dependence of the power index of the EPPs quantum content (m) on external Ca ions concentration [Ca]0 is directly proportional to the initial miniature EPP frequency and can range from 2 to 5. The increase of m due to the action of Ca ions was accompanied by the growth of P and n binomial parameters. The P parameter depended upon the first power of (Ca)0 and n parameter - upon the second power of [Ca]0. Various dynamics of m under the influence of Ca ions in sartorius neuromuscular junctions seems to be due to different increases in power of available transmitter release store.

Animals↗
PubMed1980

[Binomial parameters of mediator release in the process of facilitation of neuromuscular transmission].

The dynamics of the end-plate potentials (EPPs) facilitation at paired stimulation of motor nerve was studied in experiments with isolated neuromuscular preparations of the frog musculus sartorius. It was found that the increase in quantum content of EPPs diminished after a single impulse in two exponential phases. The first component, observed immediately after conditioning stimulation, was accompanied by an increase in the binomial parameter n (transmitter available store), and the second one, occuring after 30-60 ms,--by the growth of parameter P (probability of quantum mediator release). The obtained data are discussed in terms of calcium hypothesis of transmitter release.

Animals↗
PubMed1979

[Cooperative effect of calcium ions in freeing a mediator from the neuromuscular synapses of large and small muscle fibers of frog sartorius muscle].

The dependence of a amplitude and quantum content (m) of the end plate potentials on the external calcium concentration was studied in experiments on the frog sartorius amplitude of the miniature end plate potentials were found. The data obtained suggest that the number of calcium ions taking part in the release of each transmitter quantum may be different.

Acetylcholine↗
PubMed1979

[Mediator liberation at the neuromuscular junctions of rhythmically stimulated frog sartorius muscles].

Synapses of large fibers seem to have a more obvious initial increase followed by a greater decrease in quantum content (m) of EPPs than the small fibers. The total amount of neurotransmitter released during EPPs reproduction was much greater in the large fibres. The calculation of binomial parameters of transmitter release showed that n parameter repeated the dynamics of m, while the P parameter gradually increased. The initial uptake of P and increase of n was more obvious in verve endings of the large muscle fibres. The findings suggest an unequal length of synaptic contact.

Acetylcholine↗
PubMed1978

[Electrophysiologic, morphometric and histocytochemical characteristics of frog sartorius muscle fibers].

Three groups of muscle fibers (dark, light, and intermediate) were revealed in the fibers of the frog sartorius muscle in examination of the succinate dehydrogenase (SDH) activity. There was revealed a reverse relationship between the diameter of the muscle fibers an the SDH activity in them. The external surface of sartorius muscle is chiefly represented by dark muscle fibers, whereas the internal one--by light ones. Microelectrode study demonstrated that the fibers of the external surface were characterized, in comparison with those of the internal one, by lesser action potentials, prolonged trace negative potential, low quant composition of the end plate potentials, high amplitude and low frequency of the end plate miniature potentials. Analysis of the data obtained demonstrated definite interrelationship between the histochemical profile of the muscle fibers of the frog sartorius muscle and their electrophysiological characteristics.

Animals↗