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 (Ca(V)3.1, Ca(V)3.2 and Ca(V)3.3). Using tsA-201 cells, we demonstrate that Ca(V)3.2 current (IC50, 0.8 mu M) is significantly more sensitive to Zn2+ than are Ca(V)3.1 and Ca(V)3.3 currents (IC50, 80 mu M and similar to 160 mu M, respectively). This inhibition of Ca(V)3 currents is associated with a shift to more negative membrane potentials of both steady-state inactivation for Ca(V)3.1, Ca(V)3.2 and Ca(V)3.3 and steady-state activation for Ca(V)3.1 and Ca(V)3.3 currents. We also document changes in kinetics, especially a significant slowing of the inactivation kinetics for Ca(V)3.1 and Ca(V)3.3, but not for Ca(V)3.2 currents. Notably, deactivation kinetics are significantly slowed for Ca(V)3.3 current (similar to 100-fold), but not for Ca(V)3.1 and Ca(V)3.2 currents. Consequently, application of Zn2+ results in a significant increase in Ca(V)3.3 current in action potential clamp experiments, while Ca(V)3.1 and Ca(V)3.2 currents are significantly reduced. In neuroblastoma NG 108-15 cells, the duration of Ca(V)3.3-mediated action potentials is increased upon Zn2+ application, indicating further that Zn2+ behaves as a Ca(V)3.3 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.