Effects of amiloride and derivatives on the colonic and gastric K-ATPase activity. (A) Colonic K-ATPase activity was measured as a function of the concentration of amiloride. (B) Gastric K-ATPase activity was measured as a function of the concentration of amiloride (□, solid line), or benzamil (○, dashed line), or EIPA (△, dotted line). (C) K-ATPase activity was measured as a function of the concentration of amiloride in the absence (■, solid line) or presence of 1 μM nigericin (●, short dashed line). Values are means ± se of 3 animals.