Snapin Specifically Up-Regulates Ca1.3 Ca Channel Variant with a Long Carboxyl Terminus.

Ca entry through Ca1.3 Ca channels plays essential roles in diverse physiological events. We employed yeast-two-hybrid (Y2H) assays to mine novel proteins interacting with Ca1.3 and found Snapin2, a synaptic protein, as a partner interacting with the long carboxyl terminus (CT) of rat Ca1.3 variant. Co-expression of Snapin with Ca1.3/Caβ/αδ subunits increased the peak current density or amplitude by about 2-fold in HEK-293 cells and oocytes, without affecting voltage-dependent gating properties and calcium-dependent inactivation. However, the Snapin up-regulation effect was not found for rat Ca1.3 containing a short CT (CT) in which a Snapin interaction site in the CT was deficient. Luminometry and electrophysiology studies uncovered that Snapin co-expression did not alter the membrane expression of HA tagged Ca1.3 but increased the slope of tail current amplitudes plotted against ON-gating currents, indicating that Snapin increases the opening probability of Ca1.3. Taken together, our results strongly suggest that Snapin directly interacts with the CT of Ca1.3, leading to up-regulation of Ca1.3 channel activity via facilitating channel opening probability.