Abstract
To elucidate biophysical mechanisms underlying the Zn 2+ block on the low-threshold T-type Ca 2+ current ( I T), we examined the Zn 2+-induced alterations of gating properties of I T of a rat thalamic relay neuron and of α1G channels expressed in HEK-293 cells, using a whole-cell voltage clamp technique. The effect of Zn 2+ block depended upon holding potentials but not test potentials, indicating that, the greater the inactivation, the less Zn 2+ blocked I T. Except for the inactivation near the activation threshold of I T, no significant changes in the kinetics of activation and inactivation were induced by Zn 2+. In contrast, the rates of both de-inactivation and deactivation were dramatically increased by Zn 2+, and moreover the channels were rapidly re-blocked upon re-polarization under Zn 2+. Furthermore, the outward current via α1G channel was almost insensitive to Zn 2+. All these results imply that Zn 2+ alters the gating properties of I T mainly by accelerating its deactivation process.
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