Junctophilins contribute to the formation of junctional membrane complexes (JMCs) which link the plasma membrane with the endoplasmic or sarcoplasmic reticulum in excitable cells. Provides a structural foundation for functional cross-talk between the cell surface and intracellular calcium release channels. JPH1 contributes to the construction of the skeletal muscle triad by linking the t-tubule (transverse-tubule) and SR (sarcoplasmic reticulum) membranes. Predominantly on the plasma membrane. The transmembrane domain is anchored in endoplasmic/sarcoplasmic reticulum membrane, while the N-terminal part associates with the plasma membrane. In skeletal muscle cells, it is predominantly localized at the junction of the A and I bands. Specifically expressed in skeletal muscle. Weakly expressed in embryos and neonates. Abundant in young adult muscles. The MORN (membrane occupation and recognition nexus) repeats contribute to the plasma membrane binding, possibly by interacting with phospholipids. Mice are unable to suckle probably due to defective E-C coupling in jaw muscles, and die shortly after birth. In skeletal muscles, triad junctions are reduced in number. Mutant mice developed less contractile force and abnormal sensitivities to extracellular Ca(2+) were observed. Sarcoplasmic reticulum is often structurally abnormal. Belongs to the junctophilin family.