Polar distribution of sodium-dependent and sodium-independent transport system forl-lactate in the plasma membrane of rat enterocytes

Abstract

The uptake ofl-lactate by rat small intestinal brush-border and basal-lateral plasma membrane vesicles has been studied.l-Lactate uptake by the isolated membrane vesicles is osmotically sensitive and represents predominantly transport into an intravesicular space and not binding to the membranes. The transport ofl-lactate across the brush-border membrane is stimulated by sodium, whereas the transport across the basal-lateral plasma membrane is sodium-independent. In both types of membrane vesiclesl-lactate is transported faster thand-lactate andl-lactate transport is inhibited by α-cyano-cinnamic acid.l-Lactate transport across basal-lateral membranes is inhibited byd-lactate and pyruvate and transstimulated byl-lactate and pyruvate. The polar distribution of transport system forl-lactate in the plasma membrane of rat enterocytes—a Na⁺/l-lactate cotransport system in the brush-border membrane and a facilitated diffusion system in the basal-lateral membrane — can explain the fact that in the intact epitheliuml-lactate produced by cell metabolism is preferentially released on the serosal side and could enable the cell to perform vectorial, secondary active transport ofl-lactate from the intestinal lumen to the serosal compartment.