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AJP - Gastrointestinal and Liver Physiology, Vol 253, Issue 3 404-G410, Copyright © 1987 by American Physiological Society
ARTICLES |
C. M. Schron, R. G. Knickelbein, P. S. Aronson and J. W. Dobbins
In rabbit ileal basolateral membrane (BLM) vesicles, an outwardly directed Cl gradient ([Cl] in/out = 60/6 mM) stimulated the initial velocity of SO4 uptake compared with uptake in the absence of Cl. Under Cl gradient conditions, SO4 was transiently accumulated at a concentration twice that found at equilibrium ("overshoot"). Chloride gradient-stimulated SO4 uptake was markedly reduced by inhibitors of anion exchange (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid) and was saturable (SO4 Km = 0.302 +/- 0.064 mM; Vmax = 1.59 +/- 0.22 nmol SO4 . mg protein-1 . min-1). SO4 uptake by BLM vesicles was not stimulated by imposition of an inside-positive electrical potential, suggesting that the stimulation by a Cl gradient was not due to an induced electrical potential. Oxalate, nitrate, iodide, and bromide inhibited the initial velocity of Cl gradient-stimulated SO4 uptake, whereas phosphate, beta-hydroxybutyrate, lactate, and p-aminohippurate had no effect. When SO4 uptake by BLM vesicles was compared with that of brush-border membrane vesicles, Cl gradient-stimulated SO4 uptake was found predominantly in the BLM preparation. In conclusion, these findings provide evidence for a carrier on the ileal basolateral membrane that mediates Cl-SO4 exchange.
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