Figure 4. Voltage dependence of Ca²⁺ current activation and inactivation.

A, Ca²⁺ currents evoked by membrane depolarisations to −30 mV (trace with superimposed blue curve) and −10 mV (trace with superimposed red curve). The blue and red curves were derived assuming m² kinetics. The values of the time constant of activation (τ_m) were 0.56 ms at −30 mV and 0.33 ms at −10 mV. The value in parentheses for the scale bar refers to the trace with superimposed blue curve. B, τ_m measured at different membrane potentials (V). C, inactivation of the Ca²⁺ currents elicited by depolarisations to −30 mV (trace with superimposed blue curve) and −10 mV (trace with superimposed red curve). To facilitate comparison of the inactivation, the current amplitudes have been normalised. The value in parentheses for the scale bar refers to the trace with superimposed blue curve. The blue and red curves represent an exponential function fitted to the current using time constants of inactivation (τ_h) of 19.5 and 12.3 ms at −30 and −10 mV, respectively. D, τ_h displayed against voltage during the depolarisation (V). Note the U-shaped relationship with a minimum at 0 mV. Data are mean values ±s.e.m. from 6 experiments.