Acta Physiologica 55. (1980)
4. szám - PHYSIOLOGIA - PATHOPHYSIOLOGIA - Dankó M.-Varga E.: Sodium dependence of membrane potential oscillation induced by veratrine
Acta Physiologica Academiae Scientiarum Hungaricae, Tomus 55 (4), pp. 319 — 327 (1980) SODIUM DEPENDENCE OF MEMBRANE POTENTIAL OSCILLATION INDUCED BY VERATRINE By M. Dankó and E. Varga INSTITUTE OF PHYSIOLOGY, UNIVERSITY MEDICAL SCHOOL, DEBRECEN (Received October 29, 1979) The dependence of the membrane potential oscillation on extracellular sodium concentration was studied in the frog sartorius muscle. (1) When Na concentration of the Ringer solution was decreased to zero, the membrane potential oscillation ceased and the membrane tended to repolarize. This inhibitory effect was reversible. (2) Tetrodotoxin, 10_7 g/ml, inhibited the development of membrane potential oscillation or stopped within 2 — 4 min the membrane potential oscillation already developed, the membrane then became partly repolarized maximum to —72 mV. The inhibitory effect of tetrodotoxin was also reversible. (3) When the Na concentration of the Ringer solution was reduced to 60 mM the latency time of the membrane potential oscillation did not change. By further decreasing the Na concentration the latency time increased in a hyperbolic function. In case of 10 mM Na the latency period was 7 times longer than the control. (4) The depolarizing effect of veratrine was linearly related to the logarithm of Na concentration in a range from 10 to 120 mM Na. (5) . By decreasing the [Na]„ from 120 to 10 mM the frequency of oscillation decreased and the amplitude increased linearly as a function of the logarithm of Na concentration. In previous studies from this laboratory we reported on the depolarizing and membrane potential oscillation inducing effect of veratrine [2, 3, 13, 15, 16, 17]. It has been shown that the depolarizing effect of veratrine is Na dependent. These studies have revealed that veratrine does not depolarize the muscle membrane in a sodium free (choline) Ringer solution or in the presence of 10~7 g/ml tetrodotoxin (TTX) [13]. These observations are in agreement with those of Straub [9, 10] Wright and Tomita [18] and Ulbricht [12] who investigated the effects of veratrine on different neural structures. As far as the mechanism of the membrane potential oscillation induced by veratrine is concerned it seems important to learn whether the membrane potential oscillation is also a Na-dependent process. In the present experiments we studied this problem. Methods The experiments were performed on pairs of the sartorius muscle of Rana esculenta. The muscles were prepared under the microscope and placed into Ringer solution for 30 min before the experiments. Only the intact muscles were used. Muscles were placed into a sépara- Acta Physiologica Academiae Scientiarum Hungaricae 55, 1980