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. Required for normal organization of the triad junction, where T-tubules and the sarcoplasmic reticulum terminal cisternae are in close contact (By similarity). Required for normal skeletal muscle strength. Plays a role in excitation-contraction coupling in the heart and in regulating the rate of heart beats. {ECO:0000250|UniProtKB:E9Q9K5, ECO:0000269|PubMed:22422768}. This is the function of Ensembl gene identifier ENSG00000186439 (TRDN, triadin).