Functional analysis of the F337C mutation in the CLCN1 gene associated with dominant myotonia congenita reveals an alteration of the macroscopic conductance and voltage dependence

FIGURE 1. Subcellular localization of WT, F337C, and Q412P hClC‐1 channels. A, Schematic structure of a hClC‐1 channel subunit. The F337C mutation is located in the extracellular loop between I and J transmembrane domains. CBS is the cystathionine β‐synthase domain where ATP binds ClC‐1 and inhibits the common gating. B, Visualization of YFP‐tagged WT, F337C, or Q412P hClC‐1 channels in transfected HEK293 cells (scale bar: 5 µm). Note the clear membrane localization of WT and F337C channels, but not Q412P channels.

FIGURE 2. Functional analysis of WT and F337C hClC‐1 channels. A, Protocol used in all our experiments. B, Examples of current traces of WT, F337C, and WT/F337C hClC‐1. C, Current‐voltage curves of the instantaneous (top) and steady‐state (bottom) hClC‐1 currents. Instantaneous WT currents display an inward rectification, whereas F337C and WT/F337C currents are linear. Steady‐state F337C and WT/F337C currents are more linear than WT currents. D, Apparent Po‐voltage curve. The apparent Po was obtained by measuring the tail current at −100 mV (post‐pulse) as a function of the voltage reached during the previous step (see supporting information). The Po of F337C and WT/F337C is much less voltage‐dependent than that of WT. E. Kinetics of deactivating currents for WT, F337C, and WT/F337C hClC‐1 channels. See Eq.1 in the Methods for the fit. Each point is represented as a mean ± SEM of 9, 12, and 6 fits for WT, F337C, and WT/F337C currents, respectively. Note the reduction of the contribution of Afast and Aslow caused by the F337C mutation.