Net H+ and K+ fluxes across the apical surface of rat distal colon

The distal colon absorbs K+ (J(K)) and secretes H+ (J(H)) by what is thought to be an H+-K+-adenosinetriphosphatase (H+-K+-ATPase). However the colonic ATPase differs structurally and functionally from the gastric H+-K+-ATPase. To evaluate the link between J(H) and J(K), J(H) and J(K) were simultaneously measured with ion-specific electrodes in segments of rat distal colon. J(H) and J(K) averaged 0.40 +/- 0.03 and 0.30 +/- 0.03 mu eq . h(-1). cm(-2) (n = 191), but J(H) and J(K) did not correlate (r = 0.005, not significant). The gastric H+-K+ pump inhibitors SCK-28080 (100 mu M) and omeprazole (100 mu M): as well as a vacuolar H+-ATPase inhibitor, bafilomycin A(1) (10 mu M), did not affect J(H) or J(K). However, the Na+-K+-ATPase inhibitors ouabain (1 mM) and N-ethylmaleimide (10 mu M) inhibited J(K) but not J(H). Although 1 mM orthovanadate inhibited both J(H) and J(K), at lower concentrations orthovanadate only affected J(K). Furthermore, removing K+ from the medium did not affect J(H) Secondary hyperaldosteronism increased both J(H) and J(K); hu however, ouabain (1 mM) reduced J(K) but not J(H). Cl--free medium inhibited voltage-insensitive J(H) and voltage-sensitive J(K). Medium pH affected J(H), but that effect was contrary to the effect that pH had on Rb+ flux. These data failed to identify a relationship between J(H) and J(K) and appear to suggest that J(H) and J(K) occur by separate pathways.