The effect of the internal Na concentration on the electrogenicity of the insulin-stimulated Na,K-pump in frog skeletal muscles

Abstract

1. 1. Insulin induced a hyperpolarization of the membrane by stimulating the Na,K-pump in frog skeletal muscles. 2. 2. The Na,K-pump activity was dependent on the internal Na concentration. 3. 3. As the internal Na concentration was raised from 5mmol/kg muscle water to 18 mmol/kg muscle water, the magnitude of the insulin-induced increase in the ouabain-sensitive Na efflux (an index of the Na,K-pump activity) rose by 5-fold and the magnitude of the insulin-induced hyperpolarization rose by 8.5-fold. 4. 4. On the other hand, the specific membrane resistance was not significantly changed by a rise in the internal Na concentration. 5. 5. The Na/K coupling of the Na,K-pump was calculated at low, normal or high internal Na concentration by using the values of the insulin-induced changes in the ouabain-sensitive Na efflux and the membrane potential. 6. 6. As a result of the calculation, it was suggested that in frog skeletal muscles the Na/K coupling would increase with a rise of the internal Na concentration.