AJP - Gastrointestinal and Liver Physiology, Vol 259, Issue 4 666-G670, Copyright © 1990 by American Physiological Society

ARTICLES

Rabbit ileal brush-border membrane Cl-HCO3 exchanger is activated by an internal pH-sensitive modifier site

A. Mugharbil, R. G. Knickelbein, P. S. Aronson and J. W. Dobbins
Department of Medicine, Yale University School of Medicine, New Haven, Connecticut 06510.

The purpose of these studies was to look for evidence of a pH-sensitive modifier site on the Cl-HCO3 exchanger on the brush-border membrane in rabbit ileum utilizing membrane vesicles. When internal pH and HCO3 were increased, Cl uptake was stimulated in a sigmoidal fashion consistent with a modifier effect. Increasing internal HCO3 alone did not have a similar effect, and increasing pH alone in the absence of HCO3 resulted in very little uptake of Cl. These results suggested that OH was a poor substrate for the exchanger but that it "activated" the transport of HCO3. Further evidence for this hypothesis was provided by the observation that increasing internal pH also stimulated Cl-Cl exchange. Altering the membrane potential with K and valinomycin had no effect on Cl uptake at high internal pH, suggesting no change in the 1:1 coupling ratio for Cl-HCO3 exchange at high internal pH. These studies provide evidence that there is an internal pH-sensitive modifier site on the Cl-HCO3 exchanger.

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