Microsomal ATPase of kidney papilla: sensitivity to diuretics and other inhibitors

Microsomal ATPase isolated from rat kidney papilla was compared to that from kidney medulla. Microsomal Na, K-ATPase from papilla was more sensitive to inhibition by ouabain, Cad N-ethyl-maleimide, Hg++, Thiomerin, ethacrynic acid and Furosemide than the enzyme from the medulla. Mg-ATPase of the papilla was less sensitive than the medullary enzyme to inhibition by Ca++, Cd++, N-ethyl-maleimide, Hg++, ethacrynic acid and Furosemide. Papillary Mg-ATPase was less sensitive than papillary Na, K-ATPase to all the inhibitors mentioned. Medullary Mg-ATPase was more sensitive than medullary Na, K-ATPase to inhibition by ethacrynic acid and Furosemide but less sensitive than medullary Na, K-ATPase to all the other inhibitors. Papillary Na, K-ATPase is the most sensitive to inhibition and papillary Mg-ATPase is the most resistant to inhibition by various diuretic drugs. The possible significance of these characteristics is discussed.