Ryanodine receptor and junctional membrane structure

Abstract

In excitable cell types, activation of cell-surface Ca2+ channels triggers Ca2+ release from the endplasmic or sarcoplasmic reticulum (ER/SR). This Ca2+ signal amplification, termed Ca2+-induced or voltage-induced Ca2+ release (CICR/VICR), requires the ryanodine receptor as an intracellular Ca2+ channel, which is predominantly localized in the junctional membrane complex between the plasma membrane and the ER/SR. Junctophilin is an ER/SR membrane protein that contributes to the formation of the junctional membrane structure. Ryanodine receptor and junctophilin subtypes are derived from distinct genes and show different tissue-specific expression. Recent gene-knockout studies have defined physiological functions of both Ca2+ release via ryanodine receptors and junctional membrane structures constituted by junctophilins in excitable cells. Moreover, several human genetic diseases are caused by mutations at the ryanodine receptor and junctophilin subtype genes.