Required for normal excitation-contraction coupling in skeletal muscle and for normal muscle contraction in response to membrane depolarization. Required for normal Ca(2+) release from the sarcplasmic reticulum, which ultimately leads to muscle contraction. Probably functions via its effects on muscle calcium channels (PubMed:23736855, PubMed:29078335). Increases CACNA1S channel activity, in addition to its role in enhancing the expression of CACNA1S at the cell membrane. Has a redundant role in promoting the expression of the calcium channel CACNA1S at the cell membrane (By similarity). Slows down the inactivation rate of the calcium channel CACNA1C (PubMed:29078335). {ECO:0000250|UniProtKB:Q8BZ71, ECO:0000269|PubMed:23736855, ECO:0000269|PubMed:29078335}. This is the function of STAC3 (SH3 and cysteine rich domain 3, Ensembl gene identifier ENSG00000185482).