Net h+ and k+ fluxes across the apical surface of rat distal
colon.
Feldman, George M., and John W. Ickes, Jr.
Departments of Medicine and Physiology, McGuire Veterans Affairs
Medical Center, Medical College of Virginia / Virginia Commonwealth
University, Richmond, VA 23249
APStracts 3:0164G, 1996.
The distal colon absorbs K+ (JK) and secretes H+ (JH) by what is
thought to be an H+,K+-ATPase. However, the colonic ATPase differs
structurally and functionally from the gastric H+,K+-ATPase. To
evaluate the linkage 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 meq h-1 cm-2 and 0.30 0.03 meq h
-1 cm-2 (n = 191), but JH and JK did not correlate (r = 0.005, N.S.).
The gastric H+,K+ pump inhibitors, SCH28080 (100 mM) and omeprazole
(100 mM) as well as a vacuolar H+-ATPase inhibitor, bafilomycin A1
(10 mM), did not affect JH or JK. However, the Na+,K+-ATPase
inhibitor, ouabain (1 mM), and N-ethylmaleimide (10 mM) inhibited JK,
not JH. Although 1 mM orthovanadate inhibited both JH and JK, at
lower concentrations orthovanadate only affected JK. Furthermore,
removing K+ from the media did not affect JH. Secondary
hyperaldosteronism increased both JH and JK, but ouabain (1 mM)
reduced JK, not JH. Cl--free media 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 (20). These data
failed to identify a relationship between JH and JK, and appear to
suggest that JH and JK occur by separate pathways.
Received 17 February 1995; accepted in final form 21 August 1996.
APS Manuscript Number G73-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996