title: Cardiac sarcoplasmic reticulum calcium release and load are enhanced by subcellular cAMP elevations in PI3Kgamma-deficient mice.
abstract: We recently showed that phosphoinositide-3-kinase-gamma-deficient (PI3Kgamma-/-) mice have increased cardiac contractility without changes in heart size compared with control mice (ie, PI3Kgamma+/+ or PI3Kgamma+/-). In this study, we show that PI3Kgamma-/- cardiomyocytes have elevated Ca2+ transient amplitudes with abbreviated decay kinetics compared with control under field-stimulation and voltage-clamp conditions. When Ca2+ transients were eliminated with high Ca2+ buffering, L-type Ca2+ currents (I(Ca,L)), K+ currents, and action potential duration (APD) were not different between the groups, whereas, in the presence of Ca2+ transients, Ca2+-dependent phase of I(Ca,L) inactivation was abbreviated and APD at 90% repolarization was prolonged in PI3Kgamma-/- mice. Excitation-contraction coupling (ECC) gain, sarcoplasmic reticulum (SR) Ca2+ load, and SR Ca(2+) release fluxes measured as Ca2+ spikes, were also increased in PI3Kgamma-/- cardiomyocytes without detectable changes in Ca2+ spikes kinetics. The cAMP inhibitor Rp-cAMP eliminated enhanced ECC and SR Ca2+ load in PI3Kgamma-/- without effects in control myocytes. On the other hand, the beta-adrenergic receptor agonist isoproterenol increased I(Ca,L) and Ca2+ transient equally by approximately 2-fold in both PI3Kgamma-/- and PI3Kgamma+/- cardiomyocytes. Our results establish that PI3Kgamma reduces cardiac contractility in a highly compartmentalized manner by inhibiting cAMP-mediated SR Ca2+ loading without directly affecting other major modulators of ECC, such as AP and I(Ca,L).
authors.affiliation: Department of Physiology, Heart & Stroke Richard Lewar Centre, and Division of Cardiology, University Health Network, University of Toronto, Toronto, Canada.
authors.forename: Benoit-Gilles
authors.initials: BG
authors.lastname: Kerfant
authors.forename: Dominica
authors.initials: D
authors.lastname: Gidrewicz
authors.forename: Hui
authors.initials: H
authors.lastname: Sun
authors.forename: Gavin Y
authors.initials: GY
authors.lastname: Oudit
authors.forename: Josef M
authors.initials: JM
authors.lastname: Penninger
authors.forename: Peter H
authors.initials: PH
authors.lastname: Backx
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000502:physiology; D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054684:Cyclic Nucleotide Phosphodiesterases, Type 3; D007545:Isoproterenol; D002118:Calcium