title: Regulation of cytoplasmic pH in rat sublingual mucous acini at rest and during muscarinic stimulation.
abstract: The regulation of intracellular pH (pHi) in rat sublingual mucous acini was monitored using dual-wavelength microfluorometry of the pH-sensitive dye BCECF (2',7'-biscarboxyethyl-5(6)-carboxyfluorescein). Acini attached to coverslips and continuously superfused with HCO3(-)-containing medium (25 mM NaHCO3/5% CO2; pH 7.4) have a steady-state pHi of 7.25 +/- 0.02. Acid loading of acinar cells using the NH4+/NH3 prepulse technique resulted in a Na(+)-dependent, MIBA-inhibitable (5-(N-methyl-N-isobutyl) amiloride, Ki approximately 0.42 microM) pHi recovery, the kinetics of which were not influenced by the absence of extracellular Cl-. The rate and magnitude of the pHi recovery were dependent on the extracellular Na+ concentration, indicating that Na+/H+ exchange plays a critical role in maintaining pHi above the pH predicted for electrochemical equilibrium. When the NH4+/NH3 concentration was varied, the rate of pHi recovery was enhanced as the extent of the intracellular acidification increased, demonstrating that the activity of the Na+/H+ exchanger is regulated by the concentration of intracellular protons. Switching BCECF-loaded acini to a Cl(-)-free medium did not significantly alter resting pHi, suggesting the absence of Cl-/HCO3- exchange activity. Muscarinic stimulation resulted in a rapid and sustained cytosolic acidification (t 1/2 < 30 sec; 0.16 +/- 0.02 pH unit), the magnitude of which was amplified greater than two-fold in the presence of MIBA (0.37 +/- 0.05 pH unit) or in the absence of extracellular Na+ (0.34 +/- 0.03 pH unit). The agonist-induced intracellular acidification was blunted in HCO3(-)-free media and was inhibited by DPC (diphenylamine-2-carboxylate), an anion channel blocker. In contrast, the acidification was not influenced by removal of extracellular Cl-. The Ca2+ ionophore, ionomycin, mimicked the effects of stimulation, whereas preloading acini with BAPTA (bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid) to chelate intracellular Ca2+ blocked the agonist-induced cytoplasmic acidification. The above results indicate that during muscarinic stimulation an intracellular acidification occurs which: (i) is partially buffered by increased Na+/H+ exchange activity; (ii) is most likely mediated by HCO3- efflux via an anion channel; and (iii) requires an increase in cytosolic free [Ca2+].
authors.affiliation: Department of Dental Research, University of Rochester, New York 14642.
authors.forename: G H
authors.initials: GH
authors.lastname: Zhang
authors.forename: E J
authors.initials: EJ
authors.lastname: Cragoe
authors.forename: J E
authors.initials: JE
authors.lastname: Melvin
mesh_terms: D000345:Affinity Labels; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005452:Fluoresceins; D006863:Hydrogen-Ion Concentration; D008297:Male; D009092:Mucous Membrane / Q000378:metabolism; D010277:Parasympathomimetics / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D017923:Sodium-Hydrogen Exchangers; D013050:Spectrometry, Fluorescence; D013361:Sublingual Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000345:Affinity Labels; D002352:Carrier Proteins; D005452:Fluoresceins; D010277:Parasympathomimetics; D017923:Sodium-Hydrogen Exchangers; D004533:Egtazic Acid; D000584:Amiloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; C056369:5-(N-methyl-N-isobutyl)amiloride; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid