Creatine Transport in Brush-Border Membrane Vesicles Isolated from Rat Kidney Cortex

Abstract

Abstract. The kidney efficiently salvages creatine from the urine; however, the mechanism(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 revealed that creatine is transported into an osmotically active space and that it is also bound to the membranes. An inwardly directed NaCl gradient stimulated creatine uptake and the time course of uptake exhibited an overshoot phenomenon, which indicates the presence of an active process for creatine in these membranes. The uptake of creatine showed an absolute requirement for both Na+ and Cl-. The NaCl gradient—dependent creatine uptake was stimulated by a valinomycin-induced, inside-negative, K+-diffusion potential, which suggests that the uptake process is electrogenic. Stoichiometric analyses 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 system (Km of 15 μM). Creatine uptake was inhibited by a 100-fold excess of various compounds with the following potency order: cold creatine = guanidinopropionic acid > nipecotic acid > γ-aminobutyric acid (GABA) = β-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 > β-alanine > nipecotic acid ≫ creatine). The conclusion drawn was that the apical membrane of the renal cortical tubules contains an active, high-affinity, electrogenic, 2 Na+/1 Cl-/creatine cotransporter.