Mineralocorticoid effects on Na-K-ATPase in individual nephron segments

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Abstract
A fluorometric micromethod for the assay of Na-K-ATPase was used to determine Na-K-ATPase activity in 11 segments of the rabbit nephron. The Na-K-ATPase activity was highest (> 100 pmol .cntdot. mm-1 .cntdot. min-1) in proximal convoluted tubules (S1), medullary thick ascending limbs, distal convoluted tubules, and connecting tubules. There was a good correlation (r = 0.94) between Na-K-ATPase activity in different segments and net Na transport previously measured by in vitro tubule perfusion. Treatment of rabbits with deoxycorticosterone for 8-11 days produced increases in Na-K-ATPase activity of 100 and 500% in connecting tubules and cortical collecting ducts, respectively, without significant change in other segments. Maintenance on a low Na diet for 12-18 days was associated with a 200% increase in Na-K-ATPase activity in cortical collecting ducts only. The Na-K-ATPase activity is stimulated by mineralocorticoids in the cortical collecting duct in association with the previously observed changes in Na transport.