Transport of p-aminohippuric acid by plasma membrane vesicles isolated from rat kidney cortex

Basal-lateral plasma membrane vesicles and brush border membrane vesicles were isolated from rat kidney cortex and the uptake of p-aminohippuric acid (PAH) into these vesicles was studied by Millipore filtration techniques. Both membrane preparations take up PAH into an osmotically reactive intravesicular space. The transport across the brush border membrane seems to involve only simple diffusion whereas in the basal-lateral plasma membrane in addition a specific transport system exists which is inhibited competitively by probenecid. The apparent affinity of this transport system for PAH is 5.4 X 10(-4) M and for probenecid 5.4 X 10(-5) M. PAH uptake into basal-lateral plasma membrane vesicles is influenced by alteration of the membrane potential. Maneuvers which render the intravesicular space more positive--as for example replacement of chloride by sulfate in the presence of a sodium gradient directed into the vesicles and addition of valinomycin in the presence of a potassium gradient directed into the vesicles--stimulate the uptake of PAH. Replacement of a sodium chloride gradient by a sodium thiocyanate gradient reduces the uptake probably by reducing the inside positive membrane potential. In the absence of salt gradients anion replacement and replacement of sodium by potassium does not affect PAH transport by basal-lateral plasma membranes. These results suggest that in isolated basal-lateral membranes transfer of PAH across the membrane is accompanied by a transfer of negative charge. They furthermore provide no evidence for the existence of a sodium-PAH cotransport system in this membrane preparation.