Sodium gradient dependence of proline and glycine uptake in rat renal brush-border membrane vesicles

The sodium-dependent entry of proline and glycine into rat renal brush-border membrane vesicles was examined. The high Km system for proline shows no sodium dependence. The low Km system for glycine entry is strictly dependent on a Na+ gradient but shows no evidence of the carrier system having any affinity for Na+. The low Km system for proline and high Km system for glycine transport appear to be shared. Both systems are stimulated by a Na+ gradient and appear to have an affinity for the Na+. The effect of decreasing the Na+ concentration in the ionic gradient is to alter the Km for amino acid entry and, at low Na+ concentrations, to inhibit the V for glycine entry.