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

摘要

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 μm) is significantly more sensitive to Zn²⁺ than are CaV3.1 and CaV3.3 currents (IC50, 80 μm and ∼160 μm, 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 Ca_V3.2 currents. Notably, deactivation kinetics are significantly slowed for Ca_V3.3 current (∼100-fold), but not for Ca_V3.1 and Ca_V3.2 currents. Consequently, application of Zn²⁺ results in a significant increase in Ca_V3.3 current in action potential clamp experiments, while Ca_V3.1 and Ca_V3.2 currents are significantly reduced. In neuroblastoma NG 108-15 cells, the duration of Ca_V3.3-mediated action potentials is increased upon Zn²⁺ application, indicating further that Zn²⁺ behaves as a Ca_V3.3 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.