Proton and chloride currents in Chinese hamster ovary cells

Proton and anion conductances were studied in Chinese hamster ovary (CHO) cells using tight-seal whole-cell recording. The pipette solution contained tetramethylammonium, TMA+, methanesulfonate, MeSO3-, highly buffered to pH 5.5. An outwardly rectifying anion conductance was observed in nearly all cells, with a relative permeability of MeSO3- < or = 0.5 that of Cl-. The anion conductance was small immediately after establishing whole-cell configuration, increased rapidly to a maximum at approximately 5 min, and then decreased more slowly to a small value over tens of minutes. A small voltage-activated H+ selective conductance was observed in most cells. H+ currents were studied after the Cl- conductance has subsided. The average H+ current at +40 mV at pHo 7.0 was 1.6 pA/pF. This H+ conductance was activated by membrane depolarization and enhanced at high pHo, and exhibited activation and deactivation kinetics comparable with H+ currents in other mammalian cells.