Effect of external potassium and ouabain on sodium efflux from frog sartorius muscle.

Abstract

SummaryUsing 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 × 10-6M) 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 concentr...