Modulation of the deactivation kinetics of a recombinant rat T-type Ca(2+) channel by prior inactivation

Using patch clamp methods we have investigated the deactivation properties of the T-type Ca(2+) channel generated by expression of the rat alpha(1I) subunit in HEK293 cells. The amplitude of the repolarisation-induced tail current was strongly correlated (R=0. 998) with the current amplitude immediately prior to repolarisation. The rate of deactivation was voltage-dependent between -120 mV (tau(deact)=0.9+/-0.0 ms) and -60 mV (tau(deac)=3.3+/-0.5 ms). Interestingly, the rate of deactivation observed at -80 mV was clearly dependent on the level of inactivation induced immediately prior to repolarisation, with greater inactivation producing significantly slower deactivation. In contrast, the rate of deactivation appeared completely independent of the level of steady-state inactivation. Together these data indicate the presence of a tight relationship between the recent induction of inactivation of this T-type channel and its subsequent rate of deactivation.