Figure 1.—

Drosophila kcc mediates K⁺–Cl⁻ cotransport when expressed in Xenopus oocytes. (A) Xenopus oocytes microinjected with kcc-B, kcc-D, or control (human KCC2 or KCC4) cRNA all demonstrate uptake of ⁸⁶Rb⁺ (a congener of K⁺) under hypotonic conditions. This ⁸⁶Rb⁺ uptake is Cl⁻-dependent as it is observed in the presence (+Cl⁻, lightly shaded bars), but not in the absence (−Cl⁻, dark-shaded bars), of extracellular Cl⁻. Control oocytes microinjected with H₂0 (left) showed no Cl⁻-dependent uptake of ⁸⁶Rb⁺ under hypotonic conditions. (**) P < 0.0001 vs. water-injected control oocytes. (B) Xenopus oocytes microinjected with neither the kcc-B nor the kcc-D cRNA displayed uptake of ⁸⁶Rb⁺ under isotonic conditions that was significantly higher in the presence of Cl⁻ (+Cl⁻, light-gray bar) than in its absence (−Cl⁻, dark-shaded bar). Control oocytes microinjected with either H₂0 or human KCC4 cRNA also showed no Cl⁻-dependent uptake of ⁸⁶Rb⁺. In contrast, Xenopus oocytes microinjected with cRNA for human KCC2 demonstrate a robust Cl⁻-dependent uptake of ⁸⁶Rb⁺ under isotonic conditions. (**) P < 0.0001 vs. water-injected control oocytes