AJP - Gastrointestinal and Liver Physiology, Vol 258, Issue 2 261-G267, Copyright © 1990 by American Physiological Society

ARTICLES

Contribution of Cl(-)-OH- exchange to electroneutral NaCl absorption in rat distal colon

E. S. Foster, P. K. Dudeja and T. A. Brasitus
Department of Medicine, University of Chicago Hospitals and Clinics, Pritzker School of Medicine, Illinois 60616.

Neutral NaCl absorption is the predominant Na+ absorptive process in rat distal colon. Whether this neutral NaCl absorptive process represents Na(+)-Cl- cotransport or dual ion exchanges of Na(+)-H+ and Cl(-)-OH- has been uncertain. Recent studies using rat colonic brush-border membrane vesicles (BBMVs) have described a Na(+)-H+ exchange mechanism and have proposed that net NaCl absorption occurs via a dual ion exchange process. To date, however, an anion exchanger on the colonic apical membrane has not been identified. To determine whether a Cl(-)-OH- exchange process is present, 36Cl uptake was evaluated across rat distal colonic BBMVs. A pH gradient (7.7 in/5.5 out) stimulated active Cl- uptake. Cl- uptake was not significantly affected by the presence of a valinomycin-induced K+ diffusion potential (inside positive), suggesting that a Cl- conductive pathway is not present in these membranes. The pH gradient-stimulated Cl- uptake was a saturable function of the Cl- concentration with a Km of 14.3 +/- 5.0 mM and a Vmax of 20.4 +/- 5.5 nmol.mg protein-1.30 s-1 and was almost completely inhibited by 1 mM concentrations of SITS and DIDS, inhibitors of anion exchange processes in other epithelia. Inward gradients of Na+, K+, or Na+ and K+ did not further stimulate initial Cl- uptake, suggesting that coupling of Na+ and Cl- movement does not occur by a cotransport mechanism. Thus a Cl(-)-OH- exchange process is present in rat distal colonic BBMVs.(ABSTRACT TRUNCATED AT 250 WORDS)

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