The interaction of potassium with the activation of anomalous rectification in frog muscle membrane.

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Abstract
Inward rectification of frog muscle membrane was analyzed with the vaseline gap method. Hyperpolarization under voltage clamp produced inward K currents which had a component that activated with a time constant, .kappa.K. The activation time constant .kappa.K of the inward K currents was voltage-dependent. For a given external K concentration, the time constant was maximal for potentials near the K equilibrium potential, EK. The K chord conductance gK had a sigmoidal voltage dependency, increasing initially e-fold per 11.6 mV of hyperpolarization. When the internal K concentration was fixed, raising external K induced a shift of the .kappa.K-V and the gK-V relations in the positive direction along the voltage axis. The shift was comparable to the change in EK. No shift of the .kappa.K-V and the gK-V relations was observed when the internal K was reduced from 150 to 50 mM. Changes of internal Na concentration between 5-100 mM did not significantly affect the magnitude of inward rectification.