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

Abstract

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 comptuer 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.