Intracellular pH Regulation in Bovine Aortic Endothelial Cells: Evidence of Both Na+/H+ Exchange and Na+-Dependent Cl–/HCO–3 Exchange

Regulation of intracellular pH (pH i ) was studied in cultured bovine aortic endothelial cells, an important cell system for cardiovascular research. Suspended cells were acidified by the NH 4 Cl prepulse technique as well as by exposure to CO 2 /HCO – 3 . Subsequent rates of pH i recovery were monitored using the fluorescent dye 2′,7′-bis(2-carboxyethyl)-5-(6)-carboxyfluorescein (BCECF). In HCO – 3 -free solutions, an EIPA-sensitive, Na + -dependent mechanism fully accounted for realkalinization, namely the Na + /H + exchanger (NHE). In the presence of HCO – 3 , an additional acid efflux mechanism was found. This one was dependent on Na + and intracellular Cl – , EIPA-insensitive but DIDS-sensitive, and therefore represented a Na + -dependent Cl – /HCO – 3 exchanger (NCBE). In summary, two acid-extruding mechanisms were identified in bovine aortic endothelial cells: NHE and NCBE.