Plays a redundant role in promoting the expression of calcium channel CACNA1S at the cell membrane, and thereby contributes to increased channel activity. Slows down the inactivation rate of the calcium channel CACNA1C. Interacts (via SH3 domains) with CACNA1S (PubMed:29078335). Interacts (via SH3 domains) with CACNA1C (PubMed:29078335). Has much lower affinity for CACNA1C than for CACNA1S (PubMed:29078335). Colocalizes with CACNA1C at the plasma membrane of transfected cells.