Figure 1: Molecular functions of CLC-channels. (a) Single-channel recordings of CLC-1 showing the “double-barreled” behavior. Dotted lines depict the three current levels: C: closed state, O1: one protopore open, and O2: both protopores open. Horizontal and vertical scale bars represent 200 ms and 0.2 pA, respectively. Notice that the three current levels are separated in equi-distance. Figure, taken from Saviane et al. [42] (© Rockefeller University Press, 1999). (b) Effects of extracellular on the fast-gate open probability of the Torpedo CLC-0 Cl channel. Left panel shows single-channel recordings of CLC-0 at different extracellular concentrations indicated on the left. The calculated open probabilities of the fast gate in each concentration are shown on the right. Membrane potentials in all recordings are −60 mV. Right panel shows a summarized result for the effect on the fast-gate - curve. The extracellular concentrations are 300 mM and those indicated in the left panel. As the extracellular concentration is reduced (from 300 mM to 1 mM), the fast-gate - curve is shifted to the more depolarized membrane potential. A similar effect on the fast-gate - curve has been observed in CLC-1. Figures, taken from Chen and Miller [45] (© Rockefeller University Press, 1996).