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

1. Inward rectification of frog muscle membrane was analysed with the Vaseline gap method. 2. Hyperpolarization, under voltage clamp, produced inward potassium currents, which had a component that activated with a time constant, tau K. 3. The activation time constant tau K of the inward potassium currents was voltage dependent. For a given external potassium concentration, the time constant was maximal for potentials near the potassium equilibrium potential, EK. 4. The potassium chord conductance gK, had a sigmoidal voltage dependency, increasing initially e-fold per 11.6 mV of hyperpolarization. 5. When the internal potassium concentration was fixed, raising external potassium induced a shift of the tau K-V and the gK-V relations in the positive direction along the voltage axis. That shift was comparable to the change in EK. 6. No shift of the tau K-V and the gK-V relations was observed when the internal potassium was reduced from 150 to 50 mM. 7. Changes of internal sodium concentration between 5 and 100 mM did not significantly effect the magnitude of inward rectification.