Na~+-dependent D-mannose transport at the apical membrane of rat small intestine and kidney cortex

摘要

The presence of a Na~+/D-mannose cotransport activity in brush-border membrane vesicles (BBMV), isolated from either rat small intestine or rat kidney cortex, is examined. In the presence of an electrochemical Na~+ gradient, but not in its absence, D-mannose was transiently accumulated by the BBMV. D-Mannose uptake into the BBMV was energized by both the electrical membrane potential and the Na~+ chemical gradient. D-Mannose transport vs. external D-mannose concentration can be described by an equation that represents a superposition of a saturable component and another component that cannot be saturated up to 50 μM D-mannose. D-Mannose uptake was inhibited by D-mannose D-glucose > phlorizin, whereas for α-methyl glucopyranoside the order was D-glucose = phlorizin D-mannose. The initial rate of D-mannose uptake increased as the extravesicular Na~+ concentration increased, with a Hill coefficient of 1, suggesting that the Na~+:D-mannose cotransport stoichiometry is 1:1. It is concluded that both rat intestinal and renal apical membrane have a concentrative, saturable, electrogenic and Na~+-dependent D-mannose transport mechanism, which is different from SGLT1.