RYANODINE RECEPTOR CA2- DOES DIVERSITY IN FORM EQUAL DIVERSITY IN FUNCTION( RELEASE CHANNELS )

Complexities in calcium signaling in eukaryotic cells require diversit y in the proteins involved in generating these signals. Ln this review , we consider the ryanodine receptor (RyR) family of intracellular cal cium release channels. This includes species, tissue, and cellular dis tributions of the RyRs and mechanisms of activation, deactivation, and inactivation of RyR calcium release events. In addition, as first obs erved in nonmammalian vertebrate skeletal muscles, it is now clear tha t more than one RyR isoform is frequently coexpressed within many cell types. How multiple ryanodine receptor release channels are used to g enerate intracellular calcium transients is unknown. Therefore, a prim ary focus of this review is why more than one RyR is required for this purpose, particularly in a tissue, such as vertebrate fast-twitch ske letal muscles, where a relatively simple and straightforward change in calcium would appear to be required to elicit contraction. Finally, t he roles of the RyR isoforms and the calcium release events they media te in the development of embryonic skeletal muscle are considered.