Apical Cl- backflux in rabbit gallbladder epithelium: hydrochlorothiazide effects

We have shown that hydrochlorothiazlde (Hü 12£) inhibits the apica Na+-Cl* cotransport, reduees the intraceMular Cl‘ accumulation, abolishes the transepithelial NaC1 transport in rabbit gallbladder. Concomitantly, it seems to open an apical Cl* conductanee. To evaluate whether HCTZ dissipates the intracellular Cl* accumulation also through this parallel apical Cl* leak, the cell to lumen Cl* backflux was measured by means of the wash-out radiochemical tecnique. After a 36Cl‘ epithelial loading on the luminal side, both the tissue to mucosa (J„,) and tissue to serosa (Je) e&u.ves were determined every 2 min. Under control conditions the serosal effluxes were always higher than the mucosal ones. A compaGment analysis showed that both the serosal and ITlUCosal effluxes were sustained by two compartments. Using 25 mMSCN*, which prevents the epithelial loading, it was possible to identify the contribution of the epithelial compartment to J, and lg. The second compartment corresponded to the subepithelium. An explanation is given about the finding that the two compartments behaved as parallel and independent. After the first 4min the epithelial unloading was predominant (about 70% of the totd), so that it was possible to evaluate its changes under different conditions 2 5- 10 M HCTZ, as weû as the antibiotic nystatin, Ôcreased Jg, and this effect occurred without junctional permeability rise. TÙs Ùc rease was completely abolished by the coneomitant treatment with 10“ M SITS. ln conclusion, HCTZ dissipates Cl* intracellular accumulation wid aboûshes transepitheûal transport both inhibiting the apical Na+-Cl* symport and opening a parallel SITS-sensit ive leak for Cl*.