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 NH4Cl prepulse technique as well as by exposure to CO2/HCO3-. Subsequent rates of pH(i) recovery were monitored using the fluorescent dye 2',7'-bis(2-carboxyethyl)-5-(6)-carboxyfluorescein (BCECF). In HCO3--free solutions, an EIPA-sensitive, Na+-dependent mechanism fully accounted for realkalinization, namely the Na+/H+ exchanger (NHE). In the presence of HCO3-, 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-/HCO3- exchanger (NCBE). In summary, two acid-extruding mechanisms were identified iu bovine aortic endothelial cells: NHE and NCBE.