Mechanism of Renal Transport of L-Alanine in Luminal Membrane Vesicles

Abstract

The characteristics of L- and D-alanine transport in luminal membrane vesicles isolated either from proximal convoluted (pars convoluta) or proximal straight (pars recta) tubules were studied. Renal L- and D-alanine transport systems, displaying the following properties, were shown: In vesicles from pars convoluta, the uptake of both L- and D-alanine was mediated by both Na⁺-dependent and Na⁺-independent transport processes. It was found that an inwardly directed H⁺ gradient could drive the transport of alanine into the vesicles both in the presence and absence of Na⁺. Thus, in addition to Na⁺, the transport of L- and D-isomers of this amino acid is influenced by the H⁺ gradient. In vesicles from pars recta, the transient accumulation of L- and D-alanine was strictly dependent of Na⁺, since no ‘overshoot’ was ever observed in the absence of Na⁺.