title: Effects of intra- and extracellular H+ and Na+ concentrations on Na(+)-H+ antiport activity in the lacrimal gland acinar cells.
abstract: Kinetic properties of the Na(+)-H+ antiport in the acinar cells of the isolated, superfused mouse lacrimal gland were studied by measuring intracellular pH (pHi) and Na+ activity (aNai) with the aid of double-barreled H(+)- and Na(+)-selective microelectrodes, respectively. Bicarbonate-free solutions were used throughout. Under untreated control conditions, pHi was 7.12 +/- 0.01 and aNai was 6.7 +/- 0.6 mmol/l. The cells were acid-loaded by exposure to an NH4+ solution followed by an Na(+)-free N-methyl-D-glucamine (NMDG+) solution. Intracellular Na+ and H+ concentrations were manipulated by changing the duration of exposure to the above solutions. Subsequent addition of the standard Na+ solution rapidly increased pHi. This Na(+)-induced increase in pHi was almost completely inhibited by 0.5 mmol/l amiloride and was associated with a rapid, amiloride-sensitive increase in aNai. The rate of pHi recovery induced by the standard Na+ solution increased in a saturable manner as pHi decreased, and was negligible at pHi 7.2-7.3, indicating an inactivation of the Na(+)-H+ antiport. The apparent Km for intracellular H+ concentration was 105 nmol/l (pH 6.98). The rate of acid extrusion from the acid-loaded cells increased proportionally to the increase in extracellular pH. Depletion of aNai to less than 1 mmol/l by prolonged exposure to NMDG+ solution significantly increased the rate of Na(+)-dependent acid extrusion. The rate of acid extrusion increased as the extracellular Na+ concentration increased following Michaelis-Menten kinetics (Vmax was 0.55 pH/min and the apparent Km was 75 mmol/l at pHi 6.88).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Saito
authors.forename: T
authors.initials: T
authors.lastname: Ozawa
authors.forename: A
authors.initials: A
authors.lastname: Nishiyama
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D006859:Hydrogen / Q000378:metabolism / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007765:Lacrimal Apparatus / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D008536:Meglumine / Q000494:pharmacology; D051379:Mice; D008845:Microinjections; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D008536:Meglumine; D000584:Amiloride; D006859:Hydrogen; D012964:Sodium