Involvement of Na+-K+-ATPase in p-aminohippurate transport by rabbit kidney tissue.

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Abstract
The relation between renal accumulation of p-aminohippurate (PAH), Na+-K+-ATPase activity and the transmembranal Na+ gradient was investigated by the use of cortex slices of rabbit kidney. A moderate stimulation of PAH uptake rate was observed under anaerobic conditions in the presence of an extracellular-to-intracellular directed gradient of Na+. Inhibition of aerobic accumulation of PAH by ouabain was related to a decrease in Na+-K+-ATPase activity; this was evidenced by changes in tissue concentrations of Na+ and K+ and by measurements of high-affinity binding of ouabain to the slices. Accumulation of PAH in media with various concentrations of Na+ and K+ resembled the effect of the cations on the ATPase activity of an isolated preparation of Na+-K+-ATPase. Counteraction of the inhibitory effect of ouabain on PAH accumulation by a high concentration of K+ in the medium was related to retention of Na+-K+-ATPase activity, as evidenced by preservation of tissue-medium gradients of Na+ and K+. Data provide strong evidence for the involvement of Na+-K+-ATPase in the energization of renal PAH accumulation. Probably a metabolic (Na+-gradient-independent) component, in addition to a Na+ gradient, is essential for the attainment of high accumulation ratios of PAH by intact renal cells.