Fig. 5.

Voltage dependence of macroscopic deactivation of T-current. A, The cell was held at −120 mV and stepped every 5 sec to −50 mV for 5 msec (the activating pulse) and then to −90 to −170 mV for 30 msec (the deactivating pulse). La³⁺-subtracted currents were used to eliminate capacity transients and facilitate subsequent fitting procedures. The tail currents show larger amplitude and faster decaying kinetics as the deactivating pulse goes more negative. B, The decaying phase of tail current is fitted by monoexponential functions. The decaying time constants are 6.1 ± 1.5, 4.6 ± 0.7, 3.2 ± 0.4, 2.2 ± 0.3, 1.6 ± 0.2, 1.1 ± 0.1, 0.81 ± 0.07, 0.61 ± 0.06, and 0.47 ± 0.04 msec for deactivating potentials −90, −100, −110, −120, −130, −140, −150, −160, and −170 mV, respectively (all n = 5).C, The mean value of time constant in Bis plotted against the voltage of the deactivating pulse in a semilogarithm scale (the longitudinal axis is the natural logarithm of the deactivating time constant in milliseconds). The line is a linear fit of the form: ln(τ) = 4.77 + 0.033V, where V denotes voltage of the deactivating pulse in millivolts.