title: Apical and basolateral membrane H+ extrusion mechanisms in inner stripe of rabbit outer medullary collecting duct.
abstract: To examine mechanisms of H+ extrusion in the inner stripe of outer medullary collecting duct (OMCDIS), cell pH (pHi) was measured microfluorometrically in in vitro perfused tubules by use of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. In total absence of luminal and peritubular Na+, pHi recovery from an acid load (NH3/NH+4 pulse) occurred at an initial rate of 0.13 +/- 0.02 pH units/min, whereas in the presence of 135 mM peritubular Na+, pHi recovered at 1.40 +/- 0.28 pH units/min. Na(+)-dependent pHi recovery was completely inhibited by 1.0 mM peritubular amiloride. Luminal Na+ (135 mM) addition had no effect on pHi recovery. Na(+)-independent pHi recovery from acid load was manifest by a triphasic response: 1) initial slow alkalinization; 2) slow cell acidification; and 3) a final phase that exhibited gradually increasing rates of alkalinization, returning pHi above the initial control level (pre-NH3/NH+4 pulse). Luminal N-ethylmaleimide (NEM, 500 microM), an H(+)-ATPase inhibitor, significantly inhibited initial rate of pHi recovery and total pHi recovery; whereas 500 microM peritubular NEM had no effect on initial rate of pHi recovery. Luminal SCH 28080 (100 microM), an H(+)-K(+)-ATPase inhibitor, had no effect on initial rate of pHi recovery or total pHi recovery. Thus rabbit OMCDIS possesses both an apical membrane NEM-sensitive, SCH 28080-insensitive, Na(+)-independent H+ extrusion mechanism (likely a simple H(+)-translocating ATPase) and a basolateral membrane amiloride-sensitive Na(+)-H+ antiporter.
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas 75235.
authors.forename: S R
authors.initials: SR
authors.lastname: Hays
authors.forename: R J
authors.initials: RJ
authors.lastname: Alpern
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D006851:Hydrochloric Acid / Q000494:pharmacology; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D011522:Protons; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D013997:Time Factors
chemical_list: D007093:Imidazoles; D011522:Protons; C035235:Sch 28080; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium; D005033:Ethylmaleimide; D006851:Hydrochloric Acid