pHi regulation in Ehrlich mouse ascites tumor cells: Role of sodium-dependent and sodium-independent chloride-bicarbonate exchange

pH_i recovery in acid-loaded Ehrlich ascites tumor cells and pH_i maintenance at steady-state were studied using the fluorescent probe BCECF.Both in nominally HCO₃^–-free media and at 25 mm HCO₃^–, the measured pH_i (7.26 and 7.82, respectively) was significantly more alkaline than the pH_i. value calculated assuming the transmembrane HCO₃^–gradient to be equal to the Cl^– gradient. Thus, pH_i in these cells is not determined by the Cl^– gradient and by Cl^–/HCO₃^–exchange.pH_i recovery following acid loading by propionate exposure, NH₄⁺withdrawal, or CO₂ exposure is mediated by amiloride-sensitive Na⁺/H⁺ exchange in HCO₃^– free media, and in the presence of HCO₃^–(25 mm) by DIDS-sensitive, Na⁺-dependent Cl^–/HCO₃^–exchange. A significant residual pH_i recovery in the presence of both amiloride and DIDS suggests an additional role for a primary active H⁺ pump in pH_i regulation. pH_i maintenance at steady-state involves both Na⁺/H⁺ exchange and Na⁺-dependent Cl^–/HCO₃^–exchange.Acute removal of external Cl^– induces a DIDS-sensitive, Na⁺-dependent alkalinization, taken to represent HCO₃^–influx in exchange for cellular Cl^–. Measurements of ³⁶Cl^– efflux into Cl^–-free gluconate media with and without Na⁺ and/or HCO₃^–(10 mm) directly demonstrate a DIDS-sensitive, Na⁺dependent Cl^–/HCO₃^–exchange operating at slightly acidic pH_i (pH_o 6.8), and a DIDS-sensitive, Na⁺-independent Cl^–/HCO₃^–exchange operating at alkaline pH_i (pH_o 8.2).The excellent technical assistance of Marianne Schiødt and Birgit B. Jørgensen is gratefully acknowledged. The work was supported by the Carlsberg Foundation (B.K.) and by a grant from the Danish Natural Science Foundation (E.K.H. and L.O.S.).