Hydrogen ion cotransport by the renal brush border glutamate transporter

Sodium ion dependent glutamate transport into rabbit renal brush border membrane vesicles is stimulated by low external pH and inhibited by low internal pH. Imposition of a pH difference (delta pH) (interior alkaline) across the vesicle membrane drives glutamate accumulation in the absence of other driving forces. This process requires Na+ but is not due to generation of an Na+ gradient in response to delta pH. Internal K+ stimulates both the rate and extent of glutamate accumulation, although K+ is not absolutely required for transport. Internal H+ inhibits the rate of glutamate accumulation by decreasing this K+ stimulation. Conversely, external K+ inhibits glutamate influx, and this inhibition can be overcome by lowering the external pH. These results indicate that H+ is cotransported with glutamate and suggest the possibility that, in the absence of internal K+, H+ can also fulfill the requirement for a countertransported ion.