EFFECT OF INSULIN ON POTASSIUM EXCHANGE IN NORMAL AND OUABAIN-TREATED SKELETAL MUSCLE

¹ Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia

The addition of insulin (50 milliunits ml^-1) to sartorius muscles of winter frogs increased the uptake of K by 10% and the amount of K in the exchangeable fraction at infinite time by 21%. Although the influence of season was not studied systematically, insulin had less effect on K uptake in muscles from frogs which had not been hibernating. All of the muscle K became exchangeable when muscles were exposed to Ringer solution containing [K] which was higher (15 mEq liter^-1) or lower (K-free) than normal. Analysis of K uptake in 15 K-Ringer indicated that K moved into two intracellular compartments but K uptake was unaffected by insulin. In 1 K-Ringer, no effect of insulin on K uptake was detected by the tracer study but there was a net gain in the [K] of the insulin-treated muscles. Insulin did not influence K efflux into initially K-free Ringer. In ouabain-treated muscles, insulin decreased K uptake by 6% and caused a further reduction in the size of the exchangeable K fraction at infinite time. These observations were interpreted in terms of the active cation transport cycle. It is suggested that insulin acts on the muscle cell membrane to expose more sites (or K carriers) to K (or ouabain) without altering the channels through which K leaves the cells. Since ouabain competes with K for the carriers, ouabain inhibition of K uptake is greater in the presence of insulin than in its absence.