Unlike skeletal muscle, E-C coupling in cardiac muscle is thought to depend primarily on a mechanism called calcium-induced calcium release, which is based on the junctional structure between T-tubule and sarcoplasmic reticulum. Junctophilin-2 (JPH2) is essential to maintain this structure, as well as the integrity of T-tubule. Another protein, receptor accessory protein 5 (REEP5), functions to keep the normal morphology of junctional SR. Defects of junctional coupling can result from deficiencies of either of the two proteins. During the process of calcium-induced calcium release, RyR2s are activated by a calcium trigger, which is brought about by the flow of Ca2+ through the L-type calcium channels. After this, cardiac muscle tends to exhibit diad (or dyad) structures, rather than triads.