Subunit‐specific modulation of T‐type calcium channels by zinc

Zinc (Zn2+) functions as a signalling molecule in the nervous system and modulates many ionic channels. In this study, we have explored the effects of Zn2+ on recombinant T-type calcium channels (CaV3.1, CaV3.2 and CaV3.3). Using tsA-201 cells, we demonstrate that CaV3.2 current (IC50, 0.8 microm) is significantly more sensitive to Zn2+ than are CaV3.1 and CaV3.3 currents (IC50, 80 microm and approximately 160 microm, respectively). This inhibition of CaV3 currents is associated with a shift to more negative membrane potentials of both steady-state inactivation for CaV3.1, CaV3.2 and CaV3.3 and steady-state activation for CaV3.1 and CaV3.3 currents. We also document changes in kinetics, especially a significant slowing of the inactivation kinetics for CaV3.1 and CaV3.3, but not for CaV3.2 currents. Notably, deactivation kinetics are significantly slowed for CaV3.3 current (approximately 100-fold), but not for CaV3.1 and CaV3.2 currents. Consequently, application of Zn2+ results in a significant increase in CaV3.3 current in action potential clamp experiments, while CaV3.1 and CaV3.2 currents are significantly reduced. In neuroblastoma NG 108-15 cells, the duration of CaV3.3-mediated action potentials is increased upon Zn2+ application, indicating further that Zn2+ behaves as a CaV3.3 channel opener. These results demonstrate that Zn2+ exhibits differential modulatory effects on T-type calcium channels, which may partly explain the complex features of Zn2+ modulation of the neuronal excitability in normal and disease states.