[Variations in the sensitivity of the neuromuscular junctions of the frog to the blocking action of hyperkalemic solutions].

The depression of evoked transmitter release with solutions with enhanced (up to 8 mM) potassium concentration was studied in cut and voltage-clamped muscle fibers of frog m. cutaneous pectoris. As potassium blockade proceeds, a reduction of the second end-plate current to paired stimuli occurs before a change in the first end-plate current, the reduction of end-plate currents being simultaneous with the latency increase. The existence of variable sensitivity of different end-plates to potassium blocking action depends on year season and ionic environment. Possible mechanisms of potassium blocking action are discussed.