title: Cardiac myocyte alternans in intact heart: Influence of cell-cell coupling and β-adrenergic stimulation.
abstract: BACKGROUND
  Cardiac alternans are proarrhythmic and mechanistically link cardiac mechanical dysfunction and sudden cardiac death. Beat-to-beat alternans occur when beats with large Ca(2+) transients and long action potential duration (APD) alternate with the converse. APD alternans are typically driven by Ca(2+) alternans and sarcoplasmic reticulum (SR) Ca(2+) release alternans. But the effect of intercellular communication via gap junctions (GJ) on alternans in the intact heart remains unknown.
  
  
  OBJECTIVE
  We assessed the effects of cell-to-cell coupling on local alternans in intact Langendorff-perfused mouse hearts, measuring single myocyte [Ca(2+)] alternans synchronization among neighboring cells, and effects of β-adrenergic receptor (β-AR) activation and reduced GJ coupling.
  
  
  RESULTS
  Mouse hearts (C57BL/6) were retrogradely perfused and loaded with Fluo8-AM to record cardiac myocyte [Ca(2+)] in situ with confocal microscopy. Single cell resolution allowed analysis of alternans within the intact organ during alternans induction. Carbenoxolone (25 μM), a GJ inhibitor, significantly increased the occurrence and amplitude of alternans in single cells within the intact heart. Alternans were concordant between neighboring cells throughout the field of view, except transiently during onset. β-AR stimulation only reduced Ca(2+) alternans in tissue that had reduced GJ coupling, matching effects seen in isolated myocytes.
  
  
  CONCLUSIONS
  Ca(2+) alternans among neighboring myocytes is predominantly concordant, likely because of electrical coupling between cells. Consistent with this, partial GJ uncoupling increased propensity and amplitude of Ca(2+) alternans, and made them more sensitive to reversal by β-AR activation, as in isolated myocytes. Electrical coupling between myocytes may thus limit the alternans initiation, but also allow alternans to be more stable once established.
authors.affiliation: Department of Pharmacology, University of California, Davis, GBSF, Davis, CA 95616-8636, USA. Electronic address: karin.hammer@ukr.de.
authors.forename: Karin P
authors.initials: KP
authors.lastname: Hammer
authors.affiliation: Department of Cardiology, Medical University of Graz, Auenbruggerplatz 15, 8010 Graz, Austria. Electronic address: lj.senka@gmail.com.
authors.forename: Senka
authors.initials: S
authors.lastname: Ljubojevic
authors.affiliation: Department of Pharmacology, University of California, Davis, GBSF, Davis, CA 95616-8636, USA. Electronic address: cripplinger@ucdavis.edu.
authors.forename: Crystal M
authors.initials: CM
authors.lastname: Ripplinger
authors.affiliation: Department of Cardiology, Medical University of Graz, Auenbruggerplatz 15, 8010 Graz, Austria; Department of Cardiology, Charité - Medical University Berlin, Augustenburgerplatz 1, 13353 Berlin, Germany. Electronic address: burkert.pieske@medunigraz.at.
authors.forename: Burkert M
authors.initials: BM
authors.lastname: Pieske
authors.affiliation: Department of Pharmacology, University of California, Davis, GBSF, Davis, CA 95616-8636, USA. Electronic address: dmbers@ucdavis.edu.
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D011943:Receptors, Adrenergic, beta; D007545:Isoproterenol
keywords: Alternans; Calcium; Whole heart; β-Adrenergic receptor activation
references.citation: Biophys J. 2008 Nov 1;95(9):4469-80
references.pmid: 18658226
references.citation: Circulation. 2014 Jul 8;130(2):147-60
references.pmid: 24895455
references.citation: J Mol Cell Cardiol. 2013 May;58:100-9
references.pmid: 23104004
references.citation: Cardiovasc Res. 2011 Sep 1;91(4):598-605
references.pmid: 21613275
references.citation: Biophys J. 1999 Dec;77(6):2930-41
references.pmid: 10585917
references.citation: J Mol Cell Cardiol. 2011 Mar;50(3):510-21
references.pmid: 21145895
references.citation: Circ Res. 2002 Oct 4;91(7):585-93
references.pmid: 12364386
references.citation: J Electrocardiol. 2013 Nov-Dec;46(6):580-4
references.pmid: 23948521
references.citation: Circ Res. 1997 Oct;81(4):462-9
references.pmid: 9314826
references.citation: J Physiol. 2010 Jan 1;588(Pt 1):225-42
references.pmid: 19900959
references.citation: Heart Rhythm. 2012 Apr;9(4):600-7
references.pmid: 22100711
references.citation: Am J Physiol Heart Circ Physiol. 2008 Jan;294(1):H41-9
references.pmid: 17982010
references.citation: Cardiovasc Res. 2007 Mar 1;73(4):750-60
references.pmid: 17217937
references.citation: Cardiovasc Res. 2004 May 1;62(2):309-22
references.pmid: 15094351
references.citation: Heart Rhythm. 2011 Nov;8(11):1804-8
references.pmid: 21699870
references.citation: Sci Signal. 2014 Mar 18;7(317):ra27
references.pmid: 24643800
references.citation: Am J Physiol Heart Circ Physiol. 2010 Dec;299(6):H1843-53
references.pmid: 20889840
references.citation: J Physiol. 2000 May 1;524 Pt 3:795-806
references.pmid: 10790159
references.citation: Pacing Clin Electrophysiol. 2013 Aug;36(8):1007-16
references.pmid: 23614703
references.citation: Am J Physiol. 1985 Jun;248(6 Pt 2):H753-64
references.pmid: 2408489
references.citation: Am J Physiol. 1997 Nov;273(5 Pt 2):H2161-9
references.pmid: 9374749
references.citation: Mol Cell Biochem. 2006 Sep;289(1-2):21-9
references.pmid: 16583133
references.citation: Biophys J. 2014 Sep 16;107(6):1313-7
references.pmid: 25229139
references.citation: Nature. 2002 Jan 10;415(6868):198-205
references.pmid: 11805843
references.citation: Circulation. 1999 Mar 16;99(10):1385-94
references.pmid: 10077525
references.citation: Circ Res. 2014 Apr 25;114(9):1410-21
references.pmid: 24568740
references.citation: J Membr Biol. 2012 Aug;245(8):477-82
references.pmid: 22825715
references.citation: Circ Res. 2006 Sep 29;99(7):e65-73
references.pmid: 16960102
references.citation: J Mol Cell Cardiol. 2013 May;58:110-7
references.pmid: 23220128
references.citation: Circ Res. 2006 Sep 29;99(7):740-8
references.pmid: 16946134
references.citation: Am J Physiol Heart Circ Physiol. 2012 Oct 15;303(8):H1047-56
references.pmid: 22904161
references.citation: Cardiovasc Res. 2003 Nov 1;60(2):288-97
references.pmid: 14613858
references.citation: Pflugers Arch. 1987 Aug;409(4-5):394-402
references.pmid: 3627957
references.citation: J Cardiovasc Electrophysiol. 2004 Jun;15(6):698-709
references.pmid: 15175067
references.citation: Science. 2011 Sep 9;333(6048):1440-5
references.pmid: 21903813
references.citation: J Biol Chem. 2005 Mar 18;280(11):10646-54
references.pmid: 15615707
references.citation: PLoS One. 2013;8(12):e85365
references.pmid: 24392005
references.citation: Biophys J. 2012 Mar 21;102(6):1294-302
references.pmid: 22455912
references.citation: Cardiovasc Res. 1999 Jun;42(3):583-90
references.pmid: 10533597
references.citation: Circ Res. 2012 May 25;110(11):1454-64
references.pmid: 22539768
references.citation: Am J Physiol Heart Circ Physiol. 2009 Aug;297(2):H775-84
references.pmid: 19482965
references.citation: Heart Rhythm. 2007 May;4(5):619-26
references.pmid: 17467631
references.citation: Eur J Pharmacol. 2013 Sep 5;715(1-3):56-61
references.pmid: 23834776
references.citation: PLoS One. 2014;9(10):e111411
references.pmid: 25340795
references.citation: Am J Physiol Heart Circ Physiol. 2008 Aug;295(2):H598-609
references.pmid: 18515647
references.citation: Front Physiol. 2013 Apr 19;4:71
references.pmid: 23637684
references.citation: J Mol Cell Cardiol. 2005 Sep;39(3):419-28
references.pmid: 16026799
references.citation: Circ Res. 2004 Mar 19;94(5):650-6
references.pmid: 14752033
references.citation: J Cardiovasc Pharmacol. 2011 Jul;58(1):32-9
references.pmid: 21753256
references.citation: Circulation. 2008 Jul 1;118(1):17-25
references.pmid: 18559701
references.citation: PLoS One. 2012;7(4):e36165
references.pmid: 22577485
references.citation: J Physiol. 2002 Nov 15;545(Pt 1):65-79
references.pmid: 12433950
references.citation: Pflugers Arch. 1989 Oct;415(1):12-21
references.pmid: 2482959
references.citation: Am J Physiol Heart Circ Physiol. 2012 Jan 1;302(1):H262-9
references.pmid: 22037192
references.citation: J Membr Biol. 2012 Jun;245(5-6):319-32
references.pmid: 22739962
references.citation: Am J Physiol Heart Circ Physiol. 2002 Apr;282(4):H1534-47
references.pmid: 11893591
references.citation: J Am Coll Cardiol. 2006 Sep 19;48(6):1242-9
references.pmid: 16979013
references.citation: Exp Physiol. 2013 May;98(5):1009-27
references.pmid: 23291912
references.citation: J Mol Cell Cardiol. 2014 Dec;77:147-54
references.pmid: 25453599
references.citation: Circ Res. 2006 Mar 31;98(6):801-10
references.pmid: 16484613
references.citation: Biophys J. 2011 May 18;100(10):2356-66
references.pmid: 21575569
references.citation: Circulation. 2002 Oct 8;106(15):1968-73
references.pmid: 12370221
references.citation: PLoS One. 2011;6(6):e20310
references.pmid: 21673812