[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.