Aims: 

The slc4a10 gene product belongs to the electroneutral Na-dependent HCO3 transporters. Previous studies disagreed whether HCO3 import was Cl dependent or independent.

Methods: 

We stably transfected mouse and rat slc4a10 into NIH-3T3 fibroblast cells without endogenous Na-dependent HCO3 transport. Acid/base transport was assessed by 2',7'-bis (carboxyethyl)-5,6-carboxyfluorescein (BCECF) fluorescence microscopy. Na transport was evaluated using the Na-sensitive fluorophore CoroNa Green fluorescence microscopy. Cuvette spectrometry was applied for fast fluid exchange with the same dyes. Cl transport was determined by ³⁶Cl-efflux.

Results: 

The slc4a10 expression induced a robust Na-dependent pHi recovery in the presence of CO3/HCO3 as compared to dsRed transfected cells. This was accompanied by an increase in the intracellular Na concentration. We estimated the Na:HCO3 stoichiometry to 1:2 after almost instantaneous fluid exchange. This would suggest a negative counterion to maintain electroneutrality. Cl is the most likely counterion, as the Na-dependent pHi recovery was eliminated in the absence of extra-and intracellular Cl. Furthermore, acute extracellular Cl removal led to a substantially larger alkalization in slc4a10 cells than in control cells, while the anion exchange activity was unaltered. Finally, the Na-and HCO3 dependent Cl-efflux during pHi recovery was greater in acidified slc4a10 cells than in control cells, and was sensitive to 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS). The slc4a10 induced Cl transport rate was of the same order of magnitude as the Na and HCO3 transport.

Conclusion: 

Taken together, the rodent slc4a10 expressed in mammalian cells encodes a Na-dependent Cl/HCO3 exchanger.