Contributes to the regulation of lumenal Ca2+ release via the sarcoplasmic reticulum calcium release channels RYR1 and RYR2, a key step in triggering skeletal and heart muscle contraction (PubMed:19398037, PubMed:17846166 and PubMed:7721813). Required for normal organization of the triad junction, where T-tubules and the sarcoplasmic reticulum terminal cisternae are in close contact. Required for normal skeletal muscle strength. Plays a role in excitation-contraction coupling in the heart and in regulating the rate of heart beats (By similarity). Interacts with CASQ2 (By similarity). Homooligomer of variable subunit number; disulfide-linked. Interacts with CASQ1 and RYR1 in skeletal muscle. Additional isoforms seem to exist. Detected in skeletal muscle and in heart (at protein level). Detected in skeletal muscle and in heart. Phosphorylated by CaMK2. N-glycosylated.