[Effects of high and low doses of vitamins A and E on the excitability of frog cardiomyocytes]. / Vliianie vysokikh i nizkikh doz vitaminov A i E na vozbudimost' kardiomiotsitov liagushki.

The effects of complex vitamins A and E on electrophysiological characteristics was investigated on frog cardiomyocytes. Large doses of vitamins A and E decreased the steepness of the action potential (AP) front, decreased the spike amplitude, shortened the plateau, decreased the steepness in the last phase of AP-repolarization, and decreased the rest potential level but considerably increased overshoot. The Ap-duration decreased noticeably. Small doses of vitamins decreased the spike amplitude, shortened the plateau, decreased the Ap-duration. We assume that complex of vitamins A and E can affect the cardiomyocyte membrane transport function, mainly due to the suppression of the slow membrane channels. The AP-front increase is less steep under the influence of vitamins. It is shown that the 0-phase depolarization speed decreases due to the inhibition of sodium channels.

[Effects and high and low doses of vitamin A on the excitability of frog cardiomyocytes]. / Vliianie bol'shikh i malykh doz vitamina A na vozbudimost' kardiomiotsitov liagushki.

The effects of the vitamin A lysosomal membrane labilizator on electrophysiological characteristics was investigated on frog cardiomyocytes. Large and small doses of vitamin A produced qualitatively identical effects: decrease of the steepness of action potential (AP) front, decrease of the spike amplitude, shortening of the plateau, decrease of the steepness in the last phase of AP-repolarization. The AP-duration decreased considerably. Large doses of the vitamin also reduced the rest potential level and insignificantly increased the heart contractions frequency. We assume that vitamin A can affect the cardiomyocyte surface membrane permeability, thereby decreasing its excitability due to suppression of the sodium and potassium.

[Effects of large and small doses of vitamin E on the excitability of frog myocytes]. / Vliianie bol'shikh i malykh doz vitamina E na vozbudimost' miotsitov liagushki.

The effect of the fat-soluble vitamin E on electrophysiological characteristics was investigated on frog cardiomyocytes. Large and small doses of vitamin E produced qualitatively identical effects: shortening of the plateau and decrease of the AP--duration. We assume that large doses of vitamin E can affect the cardiomyocytes membrane transport function, mainly due to the activation of slow membrane channels.

[Influence of various agents on the magnitude of intracellular local changes of resistance]. / Vliianie vozdeistvii na velichinu vnutrikletochnykh lokal'nykh izmenenii soprotivleniia.

The effect of local changes of resistance that was earlier described in horizontal cells and muscle fibres appears in response to the changes of membrane potential. The local resistance decreased with depolarization and increased with hyperpolarization. In experiments on musculus sartorius of the frog it is shown that the magnitude of the effect increased with cooling to 0 degrees C and reversibly abolished with warming to 30--35 degrees. The effect of local changes of resistance was diminished also by ethanol (5%) and with the increase of pH of perfusing solution to 9--10, the decrease of pH to 3,5--4 increased the effect. Preincubation of the muscle in solution containing colchicine or dinitrophenol did not abolish the effect of local changes of resistance. The nature of the structure responsible for the effect is discussed.

[Intracellular local changes of resistance in muscle fibers in relation to membrane potential]. / Vnutrikletochnye lokal'nye izmeneniia soprotivleniia v myshechnykh voloknakh v zavisimosti ot membrannogo potentsiala.

Intracellular local changes of resistance in sartorius muscle of the frog were investigated. The changes of resistance that were earlier shown to be located very near to the tip of the microelectrode appear in response to the changes of membrane potential evoked in various ways: polarization with electric current, depolarization with increase of the extracellular [K+], generation of action potentials. Depolarization leads to the local decrease of resistance, hyperpolarization--to increase of it. By using the tree-barreled microelectrodes with various geometry of the cross section, an attempt was undertaken to check some spatial peculiarities of the structure responsible for the local changes of resistance.

[Effect of presynaptic neurotoxin notechis II-5 from tiger snake venom on the motor nerve endings of mice]. / Deistvie presinapticheskogo neíroktoksina notekhisa II-5 iz iada tigrovoi zmei na dvigatel'nye nervnye okonchaniia myshi.

The neurotoxin notechis II-5 (N-II-5) from tiger snake venom (Notechis scutatus) induces three-phasic changes in miniature end-plate potential (MEPP) frequency recorded in the mouse diaphragm muscle: an initial fall of frequency followed by increase and decrease in MEPP frequency up to complete blockade. The effect of N-II-5 was enhanced with rising of the solution temperature from 20 to 30 and 35 degrees C. Removal of Ca2+ from the solution prevented the presynaptic effect of N-II-5. After washing out of the muscle from N-II-5 with Ca-free solution, addition of Ca2+ to the solution provoked the development of the effect typical of the effect of typical of the toxin. In the presence of N-II-5 an increase in K+ concentration in the solution up to 20 mM did not result in a sharp rise of MEPP frequency characteristic of depolarized nerve terminals. The agents that raise Ca2+ axoplasmic concentration not on account of depolarization of nerve terminals (hypertonic solution, ionofor A23187) preserved the capacity for increasing MEPP frequecy. It is suggested that the presynaptic effect of N-II-5 is related to its phospholipase activity and can be explained by disturbance of the activity of release sites rather than by depletion of transmitter stores.

[Effect of presynaptic neurotoxins from the bee and cobra venoms on spontaneous mediator secretion from the motor nerve endings in mice]. / Vliianie presinapticheskikh neirotoksinov iz iadov pchely i kobry na spontannuiu sekretsiiu mediatora iz dvigatel'nykh nervnykh okonchanii myshi.

Phospholipases A2 (PhLA) from the bee and cobra venoms induced the three-phasic changes in miniature end-plate potential (MEPP) frequency recorded in the mouse diaphragm muscle: an initial fall of transmitter release followed by a transient increase before the final complete blockade. The removal of Ca2+ from the perfusing solution (below 10(-9) M) prevented the presynaptic effect of both PhLA. If all PhLA molecules were washed out by the Ca-free solution, the subsequent exposure to a standard solution (2 mM Ca2+) action provoked an increase in MEPP frequency. The agents capable of increasing the axoplasmic Ca concentration (ions K+, hypertonic sucrose and uncoupler--TTFB) caused the usual increase of MEPP frequency in the muscles treated with PhLA. Apparently, the presynaptic biockade induced by PhLA cannot be due to the depletion of transmitter stores.

[Responses of the neuromuscular synapses of chronically desympathized frog muscles to tetanic nerve stimulation]. / Reaktsiia nervno-myshechnogo sinapsa khronicheski desimpatizirovannoi myshtsy liagushki na tetanicheskoe razdrazhenie nerva

7--14 days after unilateral section of the abdominal sympathetic trunk, the quantum content of the end plate potential (e.p.p.) in the m. sartorius of the frog decreased. The facilitation and fluctuations of the e.p.p. amplitude during train of stimuli (20, 50, 100/sec) became more obvious. Noradrenaline (5-10(-6) g/ml) increased the amplitude of a single e.p.p. and the facilitation during repetitive stimulation. The effect of noradrenaline in sympathectomized muscles was more obvious than in the control muscles. After the noradrenaline administration, the fourfold increase of calcium concentration did not change the amplitude of e.p.p.s or the time course of the facilitation. The mechanism of depolarization--secretion coupling in the nerve terminal seems to be impaired by the sympathectomy.