Abstract
The effects of K+, Na+, and ouabain on para-aminohippurate (PAH) accumulation by rabbit kidney slices have been further examined. The present studies show that for maximum uptake of PAH to occur in Na+,K+-depleted slices extra-cellular Na+ and K+ ions are required together. Kinetic studies revealed that increasing the external K+ from 0 to 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 to 145 mM produced an increase in the V max 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 in order to inhibit active electrolyte transport showed that PAH uptake under anaerobic conditions was specifically enhanced by Na+. This stimulation occurred when cell [Na+] was less than medium [Na+]. This Na+-dependent and energy-independent accumulation of PAH was inhibited by hippuric acid but not by N-methylnicotinamide.
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