Chloride dependence of the sodium-dependent glycine transport in pig kidney cortex brush-border membrane vesicles

Abstract

The Na +-dependent glycine uptake in pig kidney cortex brush-border membrane vesicles is specifically enhanced by the presence of Cl −. The Na +-independent glycine uptake is not affected by Cl −. Various anions tested could not substitute Cl − in the activation of the Na +-dependent glycine transport. Cl − is specifically required on the outer membrane side. The Na +-dependent glycine uptake is higher in the presence of an inwardly directed Cl − gradient than the one measured in the presence of equilibrated Cl −. The Na +-dependent glycine uptake depends on, and is saturable at increasing Cl − concentrations. By studying the activation of glycine uptake by Na + in the presence and in the absence of Cl −, evidence was found that two different Na +-dependent glycine transport pathways are present in pig kidney cortex brush-border membrane vesicles. The kinetics of the glycine uptake measured in the presence of an inwardly directed NaCl gradient show the presence of two glycine transport systems, a low-affinity, high-capacity one and a high-affinity, low capacity one. In the absence of Cl − the high-affinity, low-capacity transport is almost suppressed, thus indicating the presence of a high-affinity glycine transport system simultaneously dependent on both Na + and Cl − ions.