AJP - Gastrointestinal and Liver Physiology, Vol 244, Issue 4 375-G385, Copyright © 1983 by American Physiological Society
Coupled sodium-chloride transport by rabbit ileal brush-border membrane vesicles
C. C. Fan, R. G. Faust and D. W. Powell
Uptake of Na and Cl into brush-border membrane vesicles isolated from
rabbit ileal epithelial cells was investigated with a rapid filtration
technique using 22Na and 36Cl as tracers. The rank order of anion
dependence for Na uptake in the absence of anion gradients was SCN greater
than NO3 greater than gluconate. The sequence of cation specificity for Cl
uptake was Na congruent to Li greater than K greater than choline. The
transport of Na and Cl were both inhibited by harmaline, furosemide,
4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid, and
4,4'-diisothiocyano-2,2'-stilbene disulfonic acid. Carrier mediation of
Cl-stimulated Na transport was suggested by the competition for 22Na uptake
with increasing concentrations of unlabeled Na in the presence of Cl but
not when gluconate was the counterion. Chloride-dependent Na uptake had an
apparent Km of 4.5 mM and a Vmax of 20 nmol . mg prot-1 . 15 s-1. Na-H
exchange and Cl-OH (or HCO3) exchange were also demonstrated in these
vesicles. These findings confirm the presence of an electrically neutral
carrier-mediated, Na-Cl-coupled transport process in the apical cell
membrane of rabbit ileal epithelial cells. The nature of the coupling of Na
to Cl transport, i.e., NaCl symport or a process that combines Na-H
antiport with Cl-OH (or HCO3) antiport, remains to be determined.
