Creatine transport in brush-border membrane vesicles isolated from rat kidney cortex

The kidney efficiently salvages creatine from the urine; however, the mecha nism(s) that mediates renal creatine reabsorption has not been investigated . This study characterizes the creatine transport mechanism in brush-border membrane vesicles isolated from the rat renal cortex. An osmolality plot r evealed that creatine is transported into an osmotically active space and t hat it is also bound to the membranes. An inwardly directed NaCl gradient s timulated creatine uptake and the time course of uptake exhibited an oversh oot phenomenon, which indicates the presence of an active process for creat ine in these membranes. The uptake of creatine showed an absolute requireme nt for both Na+ and Cl-. The NaCl gradient-dependent creatine uptake was st imulated by a valinomycin-induced, inside-negative, K+-diffusion potential, which suggests that the uptake process is electrogenic. Stoichiometric ana lyses indicated a probable couple ratio of 2 Na+:1 Cl-:1 creatine molecule. The kinetic study showed that creatine is transported by a high-affinity s ystem (K-m of 15 muM). Creatine uptake was inhibited by a 100-fold excess o f various compounds with the following potency order: cold creatine = guani dinopropionic acid > nipecotic acid > gamma -aminobutyric acid (GABA) = bet a -alanine = betaine, whereas carnitine, glycine, taurine, and choline were without effect. This pattern of inhibition differs from that observed for GABA uptake (unlabeled GABA = GPA > beta -alanine > nipecotic acid > creati ne). The conclusion drawn was that the apical membrane of the renal cortica l tubules contains an active, high-affinity, electrogenic, 2 Na+/1 Cl-/crea tine cotransporter.