Differences in Na and K transport in kidney cortex and medulla indicated by ouabain, ethacrynic acid and other inhibitors

The effect of various inhibitors, ouabain, ethacrynic acid (EA), thiomerin and N-ethyl maleimide (NEM) was studied on (Na + K)-ATPase in the rat kidney cortex and medulla and on sodium extrusion and potassium accumulation in slices from cortex and medulla. With each inhibitor the sensitivity of (Na + K)-ATPase in medulla was similar to that in the cortex. Mg-ATPase was more resistant than (Na + K)-ATPase to Thiomerin and NEM. Medullary Mg-ATPase was more sensitive than medullary (Na + K)-ATPase to EA. Na-extrusion and K-accumulation were completely inhibited in cortical and medullary slices by NEM. Thiomerin had no significant effect on Na extrusion or K accumulation in cortical slices: Thiomerin inhibited Na extrusion in the medulla but enhanced K-accumulation. Ouabain inhibited Na-extrusion and K-accumulation in the medulla significantly more than in the cortex. In the absence of K^- in the medium Na extrusion persisted in the cortex at 56 per cent of maximal extrusion rate while in the medulla only 30 per cent of the maximal extrusion rate persisted. EA inhibited Na-extrusion and K-accumulation significantly more in slices of cortex than in slices of kidney medulla. It is suggested that transport of sodium in kidney cortex and medulla involve quantitatively and qualitatively different mechanisms.