KINETICS AND SPECIFICITY OF L-ALANINE TRANSPORT ACROSS THE BASOLATERAL CELL-SURFACE IN ISOLATED OXYNTIC GLANDS

The time course, kinetics, specificity and sodium-dependence of alanine uptake by isolated oxyntic glands were studied. The uptake of alanine by the hydrolyzed cells was measured directly, after incubation of the glands with l-[3H]alanine. l-Alanine total influx was saturable and apparently mediated by a single entry system (Kt = 7.93 mM and Vmax = 8.0 μmol · mg-1 · 30 s-1). The Kt was comparable to previously reported values for l-alanine transport in other epithelial cells. Kinetic studies performed in the presence and absence of Na+ suggest that l-alanine uptake is mainly mediated by a Na+-dependent carrier system, but in addition, a minor diffusional component has been detected. Cross inhibition experiments performed over a wide range of concentrations (1 to 100 mM) suggest that the Na+-dependent transport system for alanine resembles system A and displays higher affinity for l-serine (Ki = 1.81 mM) than for l-alanine (K′t = 4.86 mM); a lower affinity was found for l-cysteine (Ki = 16.30 mM). Results obtained with MeAIB support the hypothesis that system A is present at the basolateral membrane of the gland cells. © 1990.