Mechanisms of Na⁺, Cl⁻, and HCO ⁻₃ Transport in the Proximal Tubule

Abstract

The general purpose of this lecture/chapter is to provide an overview of the mechanisms mediating Na⁺, Cl⁻, and HCO ⁻₃ transport in the proximal tubule of the mammalian kidney. Because this topic is so broad, attention will be focussed on four main issues concerning transport across the membranes of the proximal tubule cell: 1) mechanisms of acid secretion across the luminal membrane; 2) mechanisms of base exit across the basolateral membrane; 3) mechanisms of Cl⁻ entry across the luminal membrane; and 4) mechanisms for Cl⁻ exit across the basolateral membrane. For each of these topics, the properties of the major transport pathways determined largely (but not exclusively) on the basis of studies on isolated membrane vesicles will be correlated with the physiological roles of these same pathways as determined on the basis of studies on the intact tubule. Finally, a summary attempting to integrate these subcellular mechanisms into the overall functioning of the intact proximal tubule will be presented. Literature citations will be representative, rather than comprehensive, due to the time/space limitations imposed on this lecture/chapter.