Biphasic stimulation of amino acid uptake by glucagon in hepatocytes

Abstract

Glucagon, 1.4 μM, increased the steady-state distribution ratios of alanine and α-aminoisobutyric acid in rat hepatocytes. As a function of time, glucagon stimulated the one-min rates of uptake of alanine and α-aminoisobutyric acid in two distinct phases. In the first phase both valinomycin and glucagon rapidly increased the rate of alanine uptake in a medium containing 6 mEq/l K + but not in one containing 12 mEq/l K +. Cycloheximide did not alter the first but completely abolished the second phase of stimulation. These results indicate that the biphasic stimulation of alanine uptake in liver produced by glucagon depends upon cell membrane hyperpolarization in the first phase and on protein synthesis in the second.