Transport of L-proline and D-glucose in luminal (brush border) and contraluminal (basal-lateral) membrane vesicles from the renal cortex

The uptakes of L-proline and D-glucose by brush border and basal-lateral membranes, derived from the rabbit renal cortex tubular cell plasma membrane, represented mostly transport into an intravesicular space rather than membrane binding. A Na + electrochemical gradient (medium>vesicle) stimulated the initial rates of uptake of both the imino acid and sugar, effecting their transient movements into the membrane vesicle against concentration gradients. The uptakes of L-proline and D-glucose by basal-lateral membranes were less responsive to Na + and the relatively small stimulation could largely be accounted for by contamination of the basal-lateral membrane preparation with brush border membranes. These findings are consistent with the hypothesis that the transcellular “active” transports of L-proline and D-glucose consist of a Na + electrochemical gradient-dependent uphill influx at the luminal brush border end and a Na +-independent downhill efflux at the basal-lateral region of the tubule epithelial cell.