Snapin Specifically Up-Regulates Ca(v)1.3 Ca(2+) Channel Variant with a Long Carboxyl Terminus

Ca(2+) entry through Ca(v)1.3 Ca(2+) channels plays essential roles in diverse physiological events. We employed yeast-two-hybrid (Y2H) assays to mine novel proteins interacting with Ca(v)1.3 and found Snapin2, a synaptic protein, as a partner interacting with the long carboxyl terminus (CT(L)) of rat Ca(v)1.3(L) variant. Co-expression of Snapin with Ca(v)1.3(L)/Ca(v)β(3)/α(2)δ(2) subunits increased the peak current density or amplitude by about 2-fold in HEK-293 cells and Xenopus oocytes, without affecting voltage-dependent gating properties and calcium-dependent inactivation. However, the Snapin up-regulation effect was not found for rat Ca(v)1.3(S) containing a short CT (CT(S)) in which a Snapin interaction site in the CT(L) was deficient. Luminometry and electrophysiology studies uncovered that Snapin co-expression did not alter the membrane expression of HA tagged Ca(v)1.3(L) but increased the slope of tail current amplitudes plotted against ON-gating currents, indicating that Snapin increases the opening probability of Ca(v)1.3(L). Taken together, our results strongly suggest that Snapin directly interacts with the CT(L) of Ca(v)1.3(L), leading to up-regulation of Ca(v)1.3(L) channel activity via facilitating channel opening probability.