Snapin Specifically Up-Regulates Cav1.3 Ca<SUP>2+</SUP> Channel Variant with a Long Carboxyl Terminus

초록

Ca2+ entry through Ca(v)1.3 Ca2+ 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 (CTL) of rat Ca(v)1.3(L) variant. Co-expression of Snapin with Ca(v)1.3(L)/Ca-v beta(3)/alpha(2)delta(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 (CTS) in which a Snapin interaction site in the CTL 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 CTL of Ca(v)1.3(L), leading to up-regulation of Ca(v)1.3(L) channel activity via facilitating channel opening probability.

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