GATING OF THE VOLTAGE-DEPENDENT CHLORIDE CHANNEL CIC-O BY THE PERMEANT ANION

CHLORIDE channels of the ClC family are important for the control of m embrane excitability(1-3), cell volume regulation(4,5), and possibly t ransepithelial transport lacking the typical voltage-sensor found in c ation gating of ClC channels is clearly voltage-dependent. For the pro totype Torpedo channel ClC-0 (refs 11-15) we now show that channel ope ning is strongly facilitated by external chloride. Other less permeabl e anions can substitute for chloride with less efficiency. ClC-0 condu ctance shows an anomalous mole fraction behaviour with Cl-/NO3- mixtur es, suggesting a multi-ion pore. Gating shows a similar anomalous beha viour, tightly linking permeation to gating. Eliminating a positive ch arge at the cytoplasmic end of domain D12 changes kinetics, concentrat ion dependence and halide selectivity of gating, and alters pore prope rties such as ion selectivity, single-channel conductance and rectific ation. Taken together, our results strongly suggest that in these chan nels voltage-dependent gating is conferred by the permeating ion itsel f, acting as the gating charge.