Glucagon stimulation of hepatic Na⁺, K⁺-ATPase

Summary

In the perfused rat liver administration of glucagon was shown to result in a transiently increased uptake of K⁺, indicating the possible involvement of the Na⁺, K⁺-ATPase. Direct measurement of the activity of Na⁺, K⁺-ATPase revealed a two-fold stimulation of the enzyme by glucagon. The effect of glucagon on the activity of the enzyme was immediate. Simultaneously with the increase in the activity of the Na⁺, K⁺-ATPase, the activity of Mg²⁺-ATPase decreased. In order to evaluate whether the activation of the Na⁺, K⁺-ATPase by glucagon is related to the metabolic effects of the hormone, experimental conditions known to interfere with the activity of the enzyme were employed and glucagon stimulation of Ca²⁺-efflux, mitochondrial metabolism and gluconeogenesis were measured. K⁺-free perfusate, high K⁺ perfusate or ouabain interfered to varying degrees with the glucagon stimulation of these responses. The combination of K⁺-free perfusate and ouabain almost completely abolished the glucagon stimulation of all three parameters. These results demonstrate the glucagon stimulation of Na⁺, K⁺-ATPase and raise the possibility that the activation of the enzyme by glucagon might be a necessary link for the manifestation of its metabolic effects.