pHi regulation in Ehrlich mouse ascites tumor cells: role of sodium-dependent and sodium-independent chloride-bicarbonate exchange.
pHi recovery in acid-loaded Ehrlich ascites tumor cells and pHi maintenance at steady-state were studied using the fluorescent probe BCECF. Both in nominally HCO3(-)-free media and at 25 mM HCO3-, the measured pHi (7.26 and 7.82, respectively) was significantly more alkaline than the pHi value calculated assuming the transmembrane HCO3- gradient to be equal to the Cl- gradient. Thus, pHi in these cells is not determined by the Cl- gradient and by Cl-/HCO3- exchange. pHi 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 pHi recovery in the presence of both amiloride and DIDS suggests an additional role for a primary active H+ pump in pHi regulation. pHi 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 pHi (pHo 6.8), and a DIDS-sensitive, Na+)-independent Cl-/HCO3- exchange operating at alkaline pHi (pHo 8.2).
Kramhøft
B
B
August Krogh Institute, Copenhagen, Denmark.
Hoffmann
E K
EK
Simonsen
L O
LO
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000502:physiology*; D001639:Bicarbonates / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000473:pathology* / Q000503:physiopathology*; D027963:Chloride-Bicarbonate Antiporters; D005453:Fluorescence; D005942:Gluconates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D051379:Mice; D011422:Propionates / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D005942:Gluconates; D011422:Propionates; D002245:Carbon Dioxide; D000584:Amiloride; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid