Ryanodine receptor calcium release channels (RyRs) play central roles in controlling intracellular calcium concentrations in excitable and non-excitable cells. RyRs are located in the sarcoplasmic or endoplasmic reticulum, intracellular Ca2+ storage compartment, and release Ca2+ during cellular action potentials or in response to other cellular stimuli. Mammalian cells express three structurally related isoforms of RyR. RyR1 and RyR2 are the major RyR isoforms in skeletal and cardiac muscle, respectively, and RyR3 is expressed in various tissues along with the other two isoforms. A prominent feature of RyRs is that the Ca2+ release channel activities of RyRs are regulated by calcium ions; therefore, intracellular Ca2+ release controls positive- and negative-feedback phenomena through the RyRs. RyR channel activities are also regulated by Ca2+ indirectly, i.e. through Ca2+ binding proteins at both cytosolic and sarco/endoplasmic reticulum luminal sides. Here, I summarize Ca2+-dependent feedback regulation of RyRs including recent progress in the structure/function aspects.
Keywords: Calcium release channel; Calmodulin; Excitation-contraction coupling; Intracellular calcium; Ryanodine receptor.