Evidence for carrier-mediated Cl-SO4 exchange in rabbit ileal basolateral membrane vesicles.
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.
D000818:Animals; D000838:Anions / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004563:Electrochemistry; D007082:Ileum / Q000378:metabolism*; D007474:Ion Exchange; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000378:metabolism; D011817:Rabbits; D013431:Sulfates / Q000378:metabolism*
D000838:Anions; D002352:Carrier Proteins; D002712:Chlorides; D013431:Sulfates