AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 6 781-G787, Copyright © 1986 by American Physiological Society
Na+-H+ exchange in rat colonic brush-border membrane vesicles
E. S. Foster, P. K. Dudeja and T. A. Brasitus
To demonstrate the presence of a Na+-H+ exchange process in brush-border
membrane vesicles from rat colonocytes, the fluorescence response of
acridine orange was used to monitor the formation and dissipation of pH
gradients. An inwardly directed Na+ gradient stimulated the outward flux of
H+, whereas proton influx was stimulated by an outwardly directed Na+
gradient. Since the ionophore valinomycin in the presence of a K+ gradient
did not alter Na+-stimulated proton efflux, the interrelationship of Na+
and H+ movement could not be explained solely on the basis of a membrane
potential. Na+-stimulated proton efflux was saturable with a Km for Na+ of
20.1 +/- 1.6 mM. Inwardly directed Li+ gradients also stimulated proton
efflux, and the Km for Li+ was 30.2 +/- 1.7 mM. In contrast, impermeant
cations failed to stimulate the outward flux of H+. Amiloride (1 mM)
inhibited both Na+-stimulated proton efflux and influx. Therefore, Na+-H+
exchange is present in rat colonic brush-border membranes and has
characteristics similar to other Na+-H+ antiporters. This exchange process
may be an important mechanism for Na+ absorption in the large intestine.
