Amino acid transport in isolated rat thymocytes. Effects of divalent cations and ethanol

Abstract

In dispersed rat thymocytes neither basal alpha-aminoisobutyric acid influx nor influx stimulated by insulin, prostaglandin theophylline, or butyryl adenosine 3':5'-monophosphate (cyclic AMP) depended on extracellular calcium or magnesium. The divalent cation ionophore A23187 inhibited both basal and stimulated alpha-aminoisobutyric acid influx. The extent to which influx was inhibited depended on ionophore concentration, extracellular calcium concentration, and time but did not depend on extracellular magnesium. Significant inhibition could be detected at an ionophore concentration of 1 muM and maximal inhibition occurred with 6 muM A23187. A23187 increased cellular uptake of calcium and there was good agred calcium uptake and that for ionophore inhibition of alpha-aminoisobutyric acid influx. Incubating cells with A23187 and then adding ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N',-tetraacetic acid completely reversed ionophore-stimulated cellular calcum uptake but did not reverse inhibition of alpha-aminoisobutyric acid influx. Thus, A23187 produces irreversible inhibition of alpha-aminoisobutyric acid transport in dispersed rat thymocytes. Ethanol abolished insulin-stimulated alpha-aminoisobutyric acid influx but did not alter basal influx or that stimulated by prostaglandin E1, theophylline, or N6,O2'-dibutyryl adenosine 3':5'-monophosphate. Inhibition could be detected with 0.2% (v/v) ethanol and insulin-stimulated alpha-aminoisobutyric influx was abolished with 1% ethanol. The effect of ethanol occurred immediately and could be reversed completely. This ability of ethanol to inhibit selectively insulin-stimulated alpha-aminoisobutyric acid influx indicates that the mechanism through which insulin stimulates alpha-aminoisobutyric acid influx is functionally distinct from the stimulation produced by cyclic AMP.