Monovalent cation and ouabain effects on PAH uptake by rabbit kidney slices

Abstract

The effects of K+, Na+ and ouabain on p-aminohippurate (PAH) accumulation by rabbit kidney slices was examined. For maximum uptake of PAH to occur in Na+,K+-depleted slices extracellular Na+ and K+ ions were required together. Kinetic studies revealed that increasing the external K+ from 0-5 mM caused a decrease in the apparent Km of transport. The Vmax values were not changed significantly. In the presence of 5 mM K+, increasing Na+ concentration in the bathing medium from 0-145 mM produced an increase in the Vmax while the apparent Km remained constant. In the presence of 5 mM external K+, ouabain inhibition of PAH uptake was progressively and entirely antagonized by decreasing external Na+. Studies on kidney slices treated with ouabain in a Na+,K+-free medium to inhibit active electrolyte transport showed that PAH uptake under anaerobic conditions was specifically enhanced by Na+. This stimulation occurred when cell Na+ concentration was less than medium Na+ concentration. This Na+-dependent and energy-independent accumulation of PAH was inhibited by hippuric acid but not by N-methylnicotinamide.