Effect of External Potassium and Ouabain on Sodium Efflux from Frog Sartorius Muscle ∗

Abstract

Summary

Using paired muscles from the same animal, the effect of external K, in concentrations ranging from 2.5 to 15 mM, on the efflux of ²⁴Na from frog sartorius muscles (previously enriched in Na by overnight soaking at 5° in a K-free medium) was investigated. In agreement with the results reported by others, it was found that external K ions, over the concentration range studied, increased the rate of loss of ²⁴Na from the muscle fibers. The ratio of the rate coefficient for ²⁴Na efflux in high K media to that observed in a normal K medium (2.5 mM) was a linear function of external K concentration throughout the concentration range investigated. In media containing 2.5 mM K, ouabain (1 × 10^-6 M) completely inhibited the stimulatory effect of K on Na efflux. With 5 mM K in the medium, inhibition was incomplete and, in media containing 8 mM K or more, no significant inhibition by ouabain of the efflux of ²⁴Na was noted. These results are compatible with a competitive inhibition by ouabain, at the concentration used, of the stimulating effect of K on Na efflux in muscle.