IP3-dependent nuclear Ca2+ signalling in the mammalian heart.
In cardiac myocytes the type-2 inositol 1,4,5-trisphosphate receptor (IP(3)R2) is the predominant isoform expressed. The IP(3)R2 channel is localized to the SR and to the nuclear envelope. We studied IP(3)-dependent nuclear Ca(2+) signals ([Ca(2+)](Nuc)) in permeabilized atrial myocytes and in isolated cardiac nuclei. In permeabilized myocytes IP(3) (20 microm) and the more potent IP(3)R agonist adenophostin (5 microm) caused an elevation of [Ca(2+)](Nuc). An IP(3)-dependent increase of [Ca(2+)](Nuc) was still observed after pretreatment with tetracaine to block Ca(2+) release from ryanodine receptors (RyRs), and the effect of IP(3) was partially reversed or prevented by the IP(3)R blockers heparin and 2-APB. Isolated nuclei were superfused with an internal solution containing the Ca(2+) indicator fluo-4 dextran. Exposure to IP(3) (10 microm) and adenophostin (0.5 microm) increased [Ca(2+)](Nuc) by 25 and 27%, respectively. [Ca(2+)](Nuc) increased to higher levels than [Ca(2+)](Cyt) immediately adjacent to the outer membrane of the nuclear envelope, suggesting that a significant portion of nuclear IP(3) receptors are facing the nucleoplasm. When nuclei were pretreated with heparin or 2-APB, IP(3) failed to increase [Ca(2+)](Nuc). Isolated nuclei were also loaded with the membrane-permeant low-affinity Ca(2+) probe fluo-5N AM which compartmentalized into the nuclear envelope. Exposure to IP(3) and adenophostin resulted in a decrease of the fluo-5N signal that could be prevented by heparin. Stimulation of IP(3)R caused depletion of the nuclear Ca(2+) stores by approximately 60% relative to the maximum depletion produced by the ionophores ionomycin and A23187. The fluo-5N fluorescence decrease was particularly pronounced in the nuclear periphery, suggesting that the nuclear envelope may represent the predominant nuclear Ca(2+) store. The data indicate that IP(3) can elicit Ca(2+) release from cardiac nuclei resulting in localized nuclear Ca(2+) signals.
Zima
Aleksey V
AV
Department of Physiology, Loyola University Chicago, Maywood, IL 60153, USA.
Bare
Dan J
DJ
Mignery
Gregory A
GA
Blatter
Lothar A
LA
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002415:Cats; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006325:Heart Atria / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D066298:In Vitro Techniques; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008856:Microscopy, Fluorescence; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D009685:Nuclear Envelope / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D013748:Tetracaine / Q000494:pharmacology
D001896:Boron Compounds; D053496:Inositol 1,4,5-Trisphosphate Receptors; D049990:Membrane Transport Modulators; D019837:Ryanodine Receptor Calcium Release Channel; D013748:Tetracaine; D006493:Heparin; C109986:2-aminoethoxydiphenyl borate; D000241:Adenosine