Modulation of the deactivation kinetics of a recombinant rat T-type Ca2+ channel by prior inactivation

Using patch clamp methods we have investigated the deactivation properties of the T-type Ca2+ channel generated by expression of the rat ocr, subunit in HEK293 cells. The amplitude of the repolarisation-induced tail current w as strongly correlated (R = 0.998) with the current amplitude immediately p rior to repolarisation. The rate of deactivation was voltage-dependent betw een -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 cle arly dependent on the level of inactivation induced immediately prior to re polarisation, with greater inactivation producing significantly slower deac tivation. In contrast, the rate of deactivation appeared completely indepen dent of the level of steady-state inactivation. Together these data indicat e the presence of a tight relationship between the recent induction of inac tivation of this T-type channel and its subsequent rate of deactivation. (C ) 2000 Published by Elsevier Science Ireland Ltd.