Effects of hormones and amino acid depletion on the kinetic parameters of amino acid uptake in monolayer cultures of rat hepatocytes.

Uptake of 2-aminoisobutyric acid (AIB) at concentrations of 0.1 mM to 30 mM was examined in sodium-containing and sodium-free media in hepatocytes pretreated without hormones (control), with hormones, or with amino acid depletion. Results show that 1-minute but not 4-minute rates can be taken as initial rates for the total or sodium-dependent transport of AIB. The data for the 1-minute sodium-dependent transport of AIB were analyzed by a computer program and also by Eadie-Hofstee and Lineweaver-Burk plots, and a single saturable system was found. In the control cultures, the saturable system had a Km of 1-2 mM AIB and a Vmax of 1.2 nmoles AIB/mg protein/minute. There was an increase in the Vmax of two to three-fold after pretreating the cultures with insulin or amino acid depletion, three to four-fold with glucagon, and six to seven fold with glucagon + dexamethasone.