AJP - Gastrointestinal and Liver Physiology, Vol 272, Issue 1 54-G62, Copyright © 1997 by American Physiological Society

ARTICLES

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

G. M. Feldman and J. W. Ickes Jr
Department of Medicine, McGuire Veterans Affairs Medical Center, Medical College of Virginia, Virginia Commonwealth University, Richmond 23249, USA.

The distal colon absorbs K+ (JK) and secretes H+ (JH) 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 JH and JK, JH and JK were simultaneously measured with ion-specific electrodes in segments of rat distal colon. JH and JK averaged 0.40 +/- 0.03 and 0.30 +/- 0.03 mu eq.h-1.cm-2 (n = 191), but JH and JK did not correlate (r = 0.005, not significant). The gastric H(+)-K+ pump inhibitors SCH-28080 (100 microM) and omeprazole (100 microM), as well as a vacuolar H(+)-ATPase inhibitor, bafilomycin A1 (10 microM), did not affect JH or JK. However, the Na(+)-K(+)-ATPase inhibitors ouabain (1 mM) and N-ethylmaleimide (10 microM) inhibited JK but not JH. Although 1 mM orthovanadate inhibited both JH and JK, at lower concentrations orthovanadate only affected JK. Furthermore, removing K+ from the medium did not affect JH. Secondary hyperaldosteronism increased both JH and JK; however, ouabain (1 mM) reduced JK but not JH. Cl(-)-free medium inhibited voltage-insensitive JH and voltage-sensitive JK. Medium pH affected JH, but that effect was contrary to the effect that pH had on Rb+ flux. These data failed to identify a relationship between JH and JK and appear to suggest that JH and JK occur by separate pathways.

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