The intracellular pH (pH(i)) of a rat parotid acinar preparation was monitored using the pH-sensitive fluorescent dye, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Under resting (unstimulated) conditions both Na+/H+ exchange and CO2/HCO3- buffering contribute to the regulation of pH(i). Muscarinic stimulation (carbachol) of the acini produced a gradual rise in pH(i) (~ 0.1 unit by 10 min) possibly due to activation of the Na+/H+ exchanger. When the exchanger was blocked by amiloride or sodium removal, carbachol induced a dramatic (atropine inhibitable) decrease in PH(i) (~ 0.4 pH unit with t( 1/2 ) ≃ 0.5 min at 1 mM carbachol). The rate of this acidification was reduced by removal of exogenous HCO3- and by the carbonic anhydrase inhibitor methazolamide. Also, acini stimulated with carbachol in Cl--free solutions showed a more pronounced acidification than in the corresponding Cl--replete media. Taken together, these data indicate that the carbachol-induced acidification of rat parotid acinar cells unmasked by inhibition of the Na+/H+ exchanger is due to a rapid loss of intracellular HCO3-. Carbachol induced acidification was inhibited by the Cl- channel blocker diphenylamine 2-carboxylate but not by 4-acetomido-4'-isothiocyanostilbene-2,2'-disulfonic acid, an inhibitor of Cl-/HCO3- exchange. In addition, this acidification could not be sustained in Ca2+-free media and was totally blocked by chelation of intracellular Ca2+. Interpreted in terms of HCO3- loss, these results closely parallel the pattern of carbachol-induced Cl- release from this same preparation and indicate that HCO3- in secreted in response to muscarinic stimulation via the same or a very similar exit pathway, presumably an apical anion channel. Under normal physiological conditions the intracellular acidification resulting from HCO3- secretion is buffered by the Na+/H+ exchanger.
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|State||Published - 1 Jan 1988|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology