Na+-coupled bicarbonate transport in renal proximal tubular epithelia

Abstract

The renal proximal tubule cell is the functional unit of an epithelium that serves to maintain a normal acid–base balance by reclaiming HCO3− filtered at the glomerulus and returning it to the circulation. The proximal tubule cell performs transcellular HCO3− reabsorption by a process of H+ secretion at the luminal membrane and export of intracellular HCO3− at the basolateral membrane. The present review describes the identification and functional characterization of the major transport pathway mediating efflux of intracellular HCO3− across the basolateral membrane of the proximal tubule cell. Compelling experimental evidence obtained from investigations using isolated membrane vesicles and the perfused proximal tubule preparation is discussed that indicate this transport pathway is an electrogenic cotransport mechanism coupling transfer of Na+, HCO3−, and CO32− across the basolateral membrane. Key words: acid–base, bicarbonate reabsorption, renal epithelia.