title: Organellar junctions promote targeted Ca2+ signaling in smooth muscle: why two membranes are better than one.
abstract: Numerous cellular processes are regulated by fluctuations in the concentration of a single cation, Ca(2+). To accomplish this feat, cells have developed mechanisms that target Ca(2+) signals to specific effectors in both space, by strategically localizing effectors and ion-transporting molecules, and time, by encoding the regulation of the frequency of Ca(2+) oscillations. With an emphasis on smooth muscle, we have analyzed how the interaction of Ca(2+) transporters located on closely apposing membranes of the plasma membrane, sarcoplasmic reticulum and mitochondria provides the structural foundation for site-specific and time-specific Ca(2+) signaling. These junctional membrane complexes can either control the concentration of Ca(2+) in the microdomain that surrounds an effector molecule or deliver Ca(2+) from the translocator on one membrane to a second translocator on the opposing membrane without significant diffusion into the bulk cytosol, an event we term 'linked Ca(2+) transport'.
authors.affiliation: The Department of Pharmacology & Therapeutics, The University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
authors.forename: Damon
authors.initials: D
authors.lastname: Poburko
authors.forename: Kuo-Hsing
authors.initials: KH
authors.lastname: Kuo
authors.forename: Jiazhen
authors.initials: J
authors.lastname: Dai
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Lee
authors.forename: Cornelis
authors.initials: C
authors.lastname: van Breemen
mesh_terms: D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology*; D006801:Humans; D007365:Intercellular Junctions / Q000502:physiology*; D017136:Ion Transport / Q000502:physiology; D008928:Mitochondria / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
chemical_list: D002118:Calcium