Comparison of microsomal ATPase in the cortex, medulla and papilla of the rat kidney

1. The properties of microsomal ATPase were compared in the cortex, medulla and papilla of the rat kidney. 2. Activation of (Na+K)-dependent ATPase in the medulla was at lower potassium concentration than in the cortex or papilla. 3. (Na+K)-dependent ATPase in the papilla was more sensitive to ouabain than cortical or medullary ATPase. 4. (Na+K)-dependent ATPase in the kidney papilla was more sensitive to inhibition by calcium, cadmium and N-ethyl-maleimide than the enzyme from the kidney cortex or medulla. 5. Mg-ATPase in each region of the kidney was more resistant to inhibition by calcium, cadmium or N-ethyl-maleimide than the corresponding (Na+K)-dependent activity. 6. Mg-ATPase in the papilla was more resistant to inhibition by these inhibitors as well as by thiocyanate than the enzyme from cortex or medulla. 7. These data may suggest functional differences in the microsomal ATPase of various regions in the kidney.