Endothelin-1-induced arrhythmogenic Ca2+ signaling is abolished in atrial myocytes of inositol-1,4,5-trisphosphate(IP3)-receptor type 2-deficient mice.
Recent studies have suggested that inositol-1,4,5-trisphosphate-receptor (IP3R)-mediated Ca2+ release plays an important role in the modulation of excitation-contraction coupling (ECC) in atrial tissue and the generation of arrhythmias, specifically chronic atrial fibrillation (AF). IP3R type-2 (IP3R2) is the predominant IP3R isoform expressed in atrial myocytes. To determine the role of IP3R2 in atrial arrhythmogenesis and ECC, we generated IP3R2-deficient mice. Our results revealed that endothelin-1 (ET-1) stimulation of wild-type (WT) atrial myocytes caused an increase in basal [Ca2+]i, an enhancement of action potential (AP)-induced [Ca2+]i transients, an improvement of the efficacy of ECC (increased fractional SR Ca2+ release), and the occurrence of spontaneous arrhythmogenic Ca2+ release events as the result of activation of IP3R-dependent Ca2+ release. In contrast, ET-1 did not alter diastolic [Ca2+]i or cause spontaneous Ca2+ release events in IP3R2-deficient atrial myocytes. Under basal conditions the spatio-temporal properties (amplitude, rise-time, decay kinetics, and spatial spread) of [Ca2+]i transients and fractional SR Ca2+ release were not different in WT and IP3R2-deficient atrial myocytes. WT and IP3R2-deficient atrial myocytes also showed a significant and very similar increase in the amplitude of AP-dependent [Ca2+]i transients and Ca2+ spark frequency in response to isoproterenol stimulation, suggesting that both cell types maintained a strong inotropic reserve. No compensatory changes in Ca2+ regulatory protein expression (IP3R1, IP3R3, RyR2, NCX, SERCA2) or morphology of the atria could be detected between WT and IP3R2-deficient mice. These results show that lack of IP3R2 abolishes the positive inotropic effect of neurohumoral stimulation with ET-1 and protects from its arrhythmogenic effects.
Li
Xiaodong
X
Department of Medicine, University of California San Diego, La Jolla, CalifA 92093-0641, USA.
Zima
Aleksey V
AV
Sheikh
Farah
F
Blatter
Lothar A
LA
Chen
Ju
J
D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology* / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D020013:Calcium Signaling; D019332:Endothelin-1 / Q000494:pharmacology*; D006325:Heart Atria / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology
D015220:Calcium Channels; D019332:Endothelin-1; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear