title: Na+-H+ antiporter of rat colonic basolateral membrane vesicles.
abstract: The present experiments were conducted, using acridine orange and 22Na uptake techniques, to demonstrate the presence of an electroneutral Na+-H+ exchange process in rat colonic basolateral membrane vesicles. Results consistent with the existence of a distinct Na+-H+ antiporter in these vesicles include the following: 1) an outwardly directed Na+ gradient stimulated proton influx (Na+in, 100 mM; pHin 7.5/pHout 7.5) and an inwardly directed sodium gradient (Na+out, 5-50 mM; pHin 6.0/pHout 7.5) stimulated proton efflux; 2) sodium-stimulated proton influx was minimally decreased (approximately 10-25%) under voltage clamp conditions (addition of valinomycin in the presence of K+ on both sides of vesicles), indicating that Na+ for H+ exchange in these vesicles could not be explained solely on the basis of a membrane potential; 3) an outwardly directed proton gradient (pHin 5.5/pHout 7.5) stimulated 22Na uptake into these vesicles and a threefold "over-shoot" was observed; 4) 22Na uptake and sodium-stimulated proton efflux were saturable with a Km for Na+ of 5.8 +/- 0.9 and 7.0 +/- 0.3 mM, respectively; 5) amiloride (1 mM) significantly inhibited both sodium-stimulated proton efflux (approximately 69%) and 22Na uptake (approximately 89%), but other transport inhibitors (acetazolamide, 4-acetamido-4'isothiocyanostilbene-2,2'-disulfonic acid, and bumetanide) had no effect on 22Na uptake; 6) N-methylglucamine+ (a nonpermeant cation) did not affect pH gradient-stimulated 22Na uptake, whereas Li+ inhibited Na+ uptake; 7) an inwardly directed Li+ gradient stimulated proton efflux and the Km for Li+ was 12.5 +/- 1.5 mM. These findings establish the existence of an electroneutral Na+-H+ exchange mechanism in rat colonic basolateral membrane vesicles.
authors.affiliation: Department of Medicine, University of Chicago, Illinois.
authors.forename: P K
authors.initials: PK
authors.lastname: Dudeja
authors.forename: E S
authors.initials: ES
authors.lastname: Foster
authors.forename: T A
authors.initials: TA
authors.lastname: Brasitus
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000165:Acridine Orange; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D003106:Colon / Q000378:metabolism*; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013050:Spectrometry, Fluorescence
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D002034:Bumetanide; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D005665:Furosemide; D012964:Sodium; D000165:Acridine Orange; D000086:Acetazolamide