Abstract
Dipeptide-proton cotransport was studied in rat renal brush border membrane vesicles from animals of different ages, starting at 7 days after birth. In the presence of an inward-directed proton gradient, glycyl-sarcosine uptake exhibited the overshoot phenomenon in all age groups studied. The magnitude of the "overshoot" increased with age and maximum accumulation of glycyl-sarcosine was observed in 42-day-old rat renal brush border membrane vesicles. Kinetic studies with glycyl-sarcosine indicated changes only in maximal velocity without any significant change in the apparent affinity value during the postnatal development of the renal brush border membrane. Since the Na+-H+ exchanger located at the brush border membrane is primarily responsible for the generation of the proton gradient, the driving force for dipeptide transport, we also measured the Na+-H+ exchanger activity in rat renal brush border membrane vesicles from suckling and adult animals. The exchanger activity was significantly greater in the adult rats compared to the suckling rats. In addition, we have confirmed in the present study previous findings from other laboratories that the activities of the Na+ gradient-driven glucose and amino acid transport systems in renal brush border membrane vesicles were higher in the adult than in the suckling rats.
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