Extracellular potassium accumulation and inward-going potassium rectification in voltage clamped ventricular muscle.

Measurements of afterpotential, action potential duration, and output of a potassium-sensitive microelectrode indicate that the application of long clamp pulses (1 to 8 seconds) to frog ventricular muscle is accompanied by a change in the extracellular potassium concentration. The plot of the magnitude of the potassium accumulation against the clamped membrane potential yields an N-shaped relation similar to the "steady state" current-voltage relation. The accumulation studies confirm a strong inward-going (anomalous) potassium rectification.