title: Na+/H+ exchange in Ehrlich ascites tumor cells. Regulation by extracellular ATP and 12-O-tetradecanoylphorbol 13-acetate.
abstract: The effects of extracellular ATP and/or the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on the intracellular pH of Ehrlich ascites tumor cells were measured using both distribution of [14C]5,5-dimethyloxazolidine-2,4-dione, and the fluorescent indicator 5(6)-carboxyfluorescein. Micromolar concentrations of extracellular ATP induce a biphasic change in the intracellular pH characterized by a rapid acidification of 0.04 pH units followed by an alkalinization of 0.11 pH units. Concurrently with the alkalinization, an increase in the total cellular [Na+] from 37.5 to 45.0 mM is observed. The pH change is half-maximally activated by 0.5-2.5 microM extracellular ATP. The intracellular alkalinization, but not the initial acidification, phase requires extracellular Na+, with half-maximal alkalinization in the presence of 24-32 mM Na+, and is inhibited by amiloride. Exposure of Ehrlich ascites tumor cells to TPA alone produces a slight alkalinization of approximately 0.04 pH units. Conversely, preincubation of the cells with TPA partially inhibits the ATP-induced changes in intracellular pH. Under identical conditions TPA also inhibits the ATP-induced increase in the cytosolic [Ca2+]. The half-maximal dose for both effects is produced by 3-10 nM TPA. These data indicate that extracellular ATP triggers the activation of Na+/H+ exchange. Furthermore, activation of protein kinase C mediates at least part of the Na+/H+ exchange, although a second mechanism may also exist.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D010704:Phorbols / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D002352:Carrier Proteins; D010704:Phorbols; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D000255:Adenosine Triphosphate; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium