Functional Characterization of Transmembrane Intracellular pH Regulators and Mechanism of Alcohol-induced Intracellular Acidosis in Human Umbilical Cord Blood Stem Cell–Like Cells

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Changing intracellular pH (pHi) exerts considerable influence on many cellular functions. Different pHi regulators, such as the Na+-H+ exchanger (NHE), Na+/


symporter, and Cl−/OH− exchanger (CHE), have been identified in mature mammalian cells. The aims of the present study were to investigate the physiological mechanisms of pHi recovery and to further explore the effects of alcohol on the pHi in human umbilical cord blood CD34+ stem cell–like cells (HUCB-CD34+STs). HUCB-CD34+STs were loaded with the pH-sensitive dye, 2′,7′-bis(2-carboxethyl)-5(6)-carboxyfluorescein, to examine pHi. In isolated HUCB-CD34+STs, we found that (1) the resting pHi is 7.03 ± 0.02; (2) 2 Na+-dependent acid extruders and a Cl−-dependent acid loading carrier exist and are functional; (3) alcohol functions in a concentration-dependent manner to reduce pHi and increase NHE activity, but it does not affect CHE activity; and (4) fomepizole, a specific alcohol dehydrogenase inhibitor, does not change the intracellular acidosis and NHE activity–induced by alcohol, whereas 3-amino-1, 2,4-trizole, a specific catalase inhibitor, entirely abolishes these effects. In conclusion, we demonstrate that 2 acid extruders and 1 acid loader (most likely NHE, NBC, and CHE, respectively) functionally existed in HUCB-CD34+STs. Additionally, the intracellular acidosis is mainly caused by catalase-mediated alcohol metabolites, which provoke the activity of NHE.

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