title: Similarities and contrasts in ryanodine receptor localization and function in osteoclasts and striated muscle cells.
abstract: This review compares ryanodine receptor (RyR)-mediated Ca(2+) signaling processes in muscle and osteoclast cells. In muscle, RyR-mediated release of an intracellularly stored, sarcoplasmic reticular (SR), Ca(2+) is triggered by voltage-sensitive dihydropyridine receptor (DHPR)-L-type Ca(2+) channels either through an allosteric coupling with the RyR in skeletal muscle or a Ca(2+)-induced Ca(2+) release initiated by extracellular Ca(2+) entry in cardiac muscle. Both cell subtypes are nevertheless capable of Ca(2+)-induced SR Ca(2+) release with cardiac muscle additionally showing a store overload-induced Ca(2+) release (SOICR) driven by SR luminal Ca(2+) under some pathological conditions. Osteoclasts similarly show cytosolic Ca(2+) elevations driven by release of intracellular Ca(2+) stores that culminate in motile activity in turn modifying bone resorptive activity. However, such triggering is controlled by ambient Ca(2+) rather than membrane potential with features strongly suggestive of control by a surface membrane Ca(2+) receptor. Yet common actions of the RyR-specific agents perchlorate, dantrolene Na, ryanodine, caffeine, adenosine 3',5'-cyclic diphosphate ribose (cADPr) and ruthenium red implicate RyR in signaling in all these cell types. These findings were reconciled by reports confirming and uniquely localizing a cell surface rather than microsomal osteoclastic RyR that might itself detect ambient Ca(2+) possibly through its otherwise intraluminal positioned low-affinity Ca(2+)-binding site in parallel with the SOICR mechanism in cardiac muscle. Such a mechanism could interact with other osteoclast processes transferring Ca(2+) between cytosol, intracellular stores and extracellular space and be integrated with systemic processes regulating Ca(2+) homeostasis.
authors: Physiological Laboratory, University of Cambridge, Cambridge, UK. clh11@cam.ac.uk
authors: Christopher L-H
authors: CL
authors: Huang
authors: Li
authors: L
authors: Sun
authors: James A
authors: JA
authors: Fraser
authors: Andrew A
authors: AA
authors: Grace
authors: Mone
authors: M
authors: Zaidi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D054792:Muscle, Striated / Q000378:metabolism*; D010010:Osteoclasts / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium