Mechanisms of Sodium Transport Across Brush Border and Basolateral Membranes

Abstract

Sodium is absorbed across the intestinal epithelium by a number of processes including primary active, secondary active and passive transport processes. To quantitate the contributions of each process we have elected to study transport using membrane vesicles isolated from the brush border and basolateral surfaces of mature enterocytes. Vesicles offer the potential to measure transport kinetics under well defined experimental conditions that avoid the complications encountered in the intact epithelium due to paracellular shunts, unstirred layers, and cellular metabolism. In this review we present our studies bearing on the role of the Na/K pump, coupled transport processes, and diffusion in the absorption of sodium across the jejunum. We conclude that diffusion and cotransport with organic solutes are the major transport systems in brush borders, while the pump accounts for net Na transport out of the epithelium into the blood.