Required for normal excitation-contraction coupling in skeletal muscle and for normal muscle contraction in response to membrane depolarization (PubMed:23818578, PubMed:27621462, PubMed:29467163). Required for normal Ca(2+) release from the sarcplasmic reticulum, which ultimately leads to muscle contraction (PubMed:23818578). Probably functions via its effects on muscle calcium channels. Increases CACNA1S channel activity, in addition to its role in enhancing the expression of CACNA1S at the cell membrane (PubMed:27621462). Has a redundant role in promoting the expression of the calcium channel CACNA1S at the cell membrane (PubMed:25548159, PubMed:27621462, PubMed:29467163). Slows down the inactivation rate of the calcium channel CACNA1C (PubMed:25548159, PubMed:29363593). Interacts (via SH3 domains) with the calcium channels CACNA1S and CACNA1C (PubMed:28112192, PubMed:29467163, PubMed:29363593). Component of a calcium channel complex with CACNA1S and CACNB1 (PubMed:28112192). Component of a calcium channel complex with CACNA1C and CACNB1 (PubMed:28112192). Co-localizes with CACNA1S and CACNA1C on T-tubules. Dected in skeletal muscle, including soleus, extensor digitorum longus, tibialis anterior, quadriceps and gastrocnemius. Detected in tongue. Detected in somites and limb buds at 9.5 and 13 dpc, in embryonic limb muscle and tongue (PubMed:23626854, PubMed:23818578). Detected in tongue and diaphragm at 14.5 dpc (PubMed:23818578). Complete perinatal lethality, due to paralysis and inability to breathe (PubMed:23626854, PubMed:23818578). Embryos have a curved body with abnormal curvature of the vertebral spine and drooping forelimbs (PubMed:23626854, PubMed:23818578). They display multiple skeletal abnormalities involving ribs, sternum and costal cartilage, and strongly reduced formation of bone ridges at major muscle attachment sites (PubMed:23818578). They weigh about 15% less than wild-type at 18.5 dpc (PubMed:23626854). They do not move or respond to touch, but have a beating heart when dissected out of the uterus (PubMed:23626854). Their myofibers have altered morphology with centrally located nuclei, unlike wild-type, where the nuclei are located in the periphery of the myofibers (PubMed:23626854, PubMed:23818578). Sarcomeres have streaming Z-lines (PubMed:23626854). The diaphragm does not contract in response to membrane depolarization or electric stimulation (PubMed:23818578). Myotubes from mutant mice lack voltage-induced calcium release from the sarcoplasmic reticulum (PubMed:23818578).