PH(I) 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) ma intenance at steady-state were studied using the fluorescent probe BCE CF. Both in nominally HCO3--free media and at 25 mM HCO3-, the measure d pH(i) (7.26 and 7.82, respectively) was significantly more alkaline than the pH(i) value calculated assuming the transmembrane HCO3- gradi ent 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) recov ery following acid loading by propionate exposure, NH4+ withdrawal, or CO2 exposure is mediated by amiloride-sensitive Na+/H+ exchange in HC O3--free free media, and in the presence of HCO3- (25 mM) by DIDS-sens itive, Na+-dependent Cl-/HCO3- exchange. A significant residual pH(i) recovery in the presence of both amiloride and DIDS suggests an additi onal role for a primary active H+ pump in pH(i) regulation. pH(i) main tenance at steady-state involves both Na+/H+ exchange and Na+-dependen t Cl-/HCO3- exchange. Acute removal of external Cl- induces a DIDS-sen sitive, Na+-dependent alkalinization, taken to represent HCO3- influx in exchange for cellular Cl-. Measurements of Cl-36(-) efflux into Cl- -free gluconate media with and without Na+ and/or HCO3- (10 mM) direct ly demonstrate a DIDS-sensitive, Na+-dependent Cl-1-/HCO3- exchange op erating at slightly acidic pH(i) (pH(o), 6.8), and a DIDS-sensitive, N a+-independent Cl-/HCO3- exchange operating at alkaline pH(i) (pH(o) 8 .2).