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

The presence of a Na+/D-mannose cotransport activity in brush-border membra ne vesicles (BBMV), isolated from either rat small intestine or rat kidney cortex, is examined. In the presence of an electrochemical Na+ gradient, bu t 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 su perposition of a saturable component and another component that cannot be s aturated up to 50 muM D-mannose. D-Mannose uptake was inhibited by D-mannos e much greater thanD-glucose > phlorizin, whereas for alpha -methyl glucopy ranoside the order was D-glucose = phlorizin much greater than D-mannose. T he initial rate of D-mannose uptake increased as the extravesicular Na+ con centration 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, elect rogenic and Na+-dependent D-mannose transport mechanism, which is different from SGLT1. (C) 2001 Elsevier Science B.V. All rights reserved.