Description of the voltage-dependent properties of TRPM8 single channels and whole-cell currents at 20°C. (A) Unitary I-V plot corresponding to channel conductance of 60 ± 2 pS (solid line; n = 11 cells). An alternative measurement was also calculated (dashed line) from the values at positive membrane potentials (70 ± 3 pS; n = 11 cells). (B) Po-V dependence (circles; n = 22 cells) was approximated by the Boltzmann relation with 111 mV for V1/2 and –34.3 mV for the slope. The triangles plot averaged whole-cell conductance at the same test potentials (ramp protocol from −100 to 120 mV; n = 10 cells). (C) Po plotted on a logarithmic scale against membrane potential to calculate the effective gating charge, giving an approximate value of 0.7 eo at room temperature. (D) Mean open- and closed-interval durations change with membrane potential. Mean open times (open circles) increased from 0.34 ± 0.01 to 2.11 ± 0.30 ms (n = 9 cells; paired t test, P < 0.01), and mean closed times (closed circles) decreased from 235 ± 37 to 1.77 ± 0.49 ms (n = 9 cells; paired t test, P < 0.01) between −100 and 140 mV, respectively. Both curves were fitted with single exponentials (open-time constant = 96 mV per e-fold change; closed-time constant = 40 mV per e-fold change). Error bars (SEM) were not plotted when they were smaller than the symbols. Dashed lines in B–D are model predictions (see Results).
