Effects of Ouabain on Na Efflux in High Internal Na and Insulin-preincubated Muscles

Abstract

To gain an insight into the mechanism of stimulation by insulin of Na efflux, the effect of high concentrations of internal Na on the inhibition by ouabain of Na efflux was compared to the inhibition by ouabain of insulin-stimulated Na efflux. The rate coefficient of 22Na efflux from high-Na muscle [Rana catesbeiana] exposed to ouabain was lower than that from low-Na muscle exposed to ouabain. The rate of net Na loss from the high-Na muscle which were exposed to ouabain was lower than that from the low-Na muscle. Na transport units whose internal Na-binding sites were occupied by Na are susceptible to ouabain. The insulin-stimulated Na efflux was inhibited by ouabain to a larger extent than was the Na efflux from the control muscle, but the final level of the rate coefficient of 22Na efflux from the muscle exposed to both insulin and ouabain was not always lower than that from the muscle exposed only to ouabain. The similarity between the effects of ouabain in high-Na muscle and in insulin-preincubated muscle suggests that insulin increases the fraction of Na transport units whose internal Na-binding sites were occupied by Na.