title: Structural evidence for perinuclear calcium microdomains in cardiac myocytes.
abstract: At each heartbeat, cardiac myocytes are activated by a cytoplasmic Ca(2+) transient in great part due to Ca(2+) release from the sarcoplasmic reticulum via ryanodine receptors (RyRs) clustered within calcium release units (peripheral couplings/dyads). A Ca(2+) transient also occurs in the nucleoplasm, following the cytoplasmic transient with some delay. Under conditions where the InsP3 production is stimulated, these Ca(2+) transients are regulated actively, presumably by an additional release of Ca(2+) via InsP3 receptors (InsP3Rs). This raises the question whether InsP3Rs are appropriately located for this effect and whether sources of InsP3 and Ca(2+) are available for their activation. We have defined the structural basis for InsP3R activity at the nucleus, using immunolabeling for confocal microscopy and freeze-drying/shadowing, T tubule "staining" and thin sectioning for electron microscopy. By these means we establish the presence of InsP3R at the outer nuclear envelope and show a close spatial relationship between the nuclear envelope, T tubules (a likely source of InsP3) and dyads (the known source of Ca(2+)). The frequency, distribution and distance from the nucleus of T tubules and dyads appropriately establish local perinuclear Ca(2+) microdomains in cardiac myocytes.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia, PA 19104-6058, USA.
authors.forename: Matias
authors.initials: M
authors.lastname: Escobar
authors.forename: Cesar
authors.initials: C
authors.lastname: Cardenas
authors.forename: Kristen
authors.initials: K
authors.lastname: Colavita
authors.forename: Nataliya B
authors.initials: NB
authors.lastname: Petrenko
authors.forename: Clara
authors.initials: C
authors.lastname: Franzini-Armstrong
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal / Q000379:methods; D008854:Microscopy, Electron / Q000379:methods; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009685:Nuclear Envelope / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D019837:Ryanodine Receptor Calcium Release Channel; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D002118:Calcium