Distal tubule bicarbonate transport.

The superficial cortical distal tubule, accessible to in vivo micropuncture and microperfusion, has been the site of a considerable number of investigations. An important fraction of renal tubule bicarbonate reabsorption, about 8 to 9% of the filtered load of this ion in the rat, takes place in this segment. The present review addresses several aspects of bicarbonate transport by distal tubule. It includes the overall magnitude of bicarbonate reabsorption, as well as the most important methods used to measure this process. The acid-base transporters responsible for transmembrane and transepithelial bicarbonate transport are also discussed. This analysis is followed by a description of several important factors that regulate bicarbonate transport in distal tubule, including the role of carbonic anhydrase and potassium depletion, and finally the participation of peptide hormones, in particular angiotensin II and arginine vasopressin. The analysis of the role of these factors is centered on microperfusion studies and on the analysis of cellular function based on cell pH and calcium modulation in renal cells in culture.