Coupled Na+-H+ exchange in isolated acinar cells from rat exocrine pancreas.
Isolated acinar cells from the rat exocrine pancreas were loaded with 6-carboxyfluorescein diacetate (CFDA), and the intracellular pH (pHi) was estimated from the pH-dependent fluorescence intensity of trapped 6-carboxyfluorescein liberated from CFDA by intracellular esterases. The intracellular fluorescence intensity was calibrated by equilibrating the internal and external pH with nigericin in K+ buffers. In the absence of Na+ (130 mmol/l K+) a pHi of 6.86 +/- 0.04 was found; in its presence (130 mmol/l Na+) a pHi of 7.17. Acute addition of Na+ increased intracellular pH with increasing Na+ concentrations, reaching a maximum at 150 mmol/l with an apparent Km of approximately 40 mmol/l. Of the different cations tested on pHi, such as Li+, K+, Rb+, and Cs+, only Li+ showed an effect on pHi similar to that of Na+. Amiloride dose dependently inhibited both Na+- and Li+-induced alkalinization (apparent Km approximately 10(-5) mol/l). In the presence of ouabain pHi was decreased by 0.2 pH units. Intracellular acidification induced by permeable buffers such as acetic acid-acetate or CO2-HCO3- was dissipated more rapidly in the presence of Na+ compared with K+ or with Na+ and amiloride in the medium. In Li+-preincubated cells intracellular acidification was higher in the absence of Li+ in the extracellular medium than in its presence. This Li+ gradient-induced acidification was dependent on the extracellular pH, was highest at an extracellular pH of 7.05, and decreased with increasing pH to 7.5. The results allow the conclusion that a coupled Na+-H+ exchange is present in pancreatic acinar cells and that the intracellular pH rather than the extracellular Na+ concentration regulates this transport mechanism.
Hellmessen
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W
Christian
A L
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Fasold
H
H
Schulz
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D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D001693:Biological Transport, Active; D002414:Cations, Monovalent; D000242:Cyclic AMP / Q000502:physiology; D005452:Fluoresceins; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D009550:Nigericin; D010042:Ouabain / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D001639:Bicarbonates; D002414:Cations, Monovalent; D005452:Fluoresceins; D011522:Protons; C027780:carboxyfluoresceindiacetate; D010042:Ouabain; D000968:Antimycin A; D000584:Amiloride; D012964:Sodium; D000242:Cyclic AMP; D009550:Nigericin; D011188:Potassium