Fig. 1.

Voltage-dependence of wild-type and F167L, A531V, and G190S myotonic hClC-1 channels in high intracellular chloride. A) Chloride currents were recorded in HEK293 cells transfected with wild-type, F167L, or A531V hClC-1 variants. Cells were held at 0 mV and 400 ms voltage pulses were applied from − 200 to + 120 mV in 10-mV intervals every 3 s. For clarity only current traces obtained every 20 mV are shown. Chloride currents displayed similar kinetics, but A531V had reduced amplitude. B) Voltage pulses were applied from − 120 to + 200 mV to elicit chloride currents in HEK293 cells expressing G190S hClC-1 variant. C) The instantaneous currents were measured at the beginning of test voltage pulses, normalized with respect to cell capacitance (pA/pF), and reported as a function of voltage. Each point is the mean ± SEM from 10 to 36 cells. The relationships show strong inward rectification for WT, F167L, and A531V channels, although current density was greatly reduced for A531V. The relationship for G190S channels was linear. D) Steady-state currents were measured at the end of test voltage pulses and reported as mean current density ± SEM in function of voltage. The WT and F167L relationships were very similar, while A531V generated reduced current densities. The G190S relationship shows a strong outward rectification. E) The voltage dependence of activation was determined by plotting the apparent open probability (Po), calculated from tail currents measured at − 105 mV, as a function of test voltage pulses. The relationships obtained from averaged data were fit with a Boltzmann equation, and fit parameters are reported in Table 1. The activation curves for WT, F167L, and A531V were superimposable, whereas G190S channels displayed a positively-shifted voltage dependence.