title: Phosphatidylinositol 3-kinase offsets cAMP-mediated positive inotropic effect via inhibiting Ca2+ influx in cardiomyocytes.
abstract: Phosphoinositide 3-kinase (PI3K) has been implicated in beta2-adrenergic receptor (beta2-AR)/G(i)-mediated compartmentation of the concurrent G(s)-cAMP signaling, negating beta2-AR-induced phospholamban phosphorylation and the positive inotropic and lusitropic responses in cardiomyocytes. However, it is unclear whether PI3K crosstalks with the beta1-AR signal transduction, and even more generally, with the cAMP/PKA pathway. In this study, we show that selective beta1-AR stimulation markedly increases PI3K activity in adult rat cardiomyocytes. Inhibition of PI3K by LY294002 significantly enhances beta1-AR-induced increases in L-type Ca2+ currents, intracellular Ca2+ transients, and myocyte contractility, without altering the receptor-mediated phosphorylation of phospholamban. The LY294002 potentiating effects are completely prevented by betaARK-ct, a peptide inhibitor of beta-adrenergic receptor kinase-1 (betaARK1) as well as G(betagamma) signaling, but not by disrupting G(i) function with pertussis toxin. Moreover, forskolin, an adenylyl cyclase activator, also elevates PI3K activity and inhibition of PI3K enhances forskolin-induced contractile response in a betaARK-ct sensitive manner. In contrast, PI3K inhibition affects neither the basal contractility nor high extracellular Ca2+-induced increase in myocyte contraction. These results suggest that beta1-AR stimulation activates PI3K via a PKA-dependent mechanism, and that G(betagamma) and the subsequent activation of betaARK1 are critically involved in the PKA-induced PI3K signaling which, in turn, negates cAMP-induced positive inotropic effect via inhibiting sarcolemmal Ca2+ influx and the subsequent increase in intracellular Ca2+ transients, without altering the receptor-mediated phospholamban phosphorylation, in intact cardiomyocytes.
authors.affiliation: Laboratory of Cardiovascular Science, Gerontology Research Center, National Institute on Aging, NIH, Baltimore, Md 21224, USA.
authors.forename: Veronique
authors.initials: V
authors.lastname: Leblais
authors.forename: Su-Hyun
authors.initials: SH
authors.lastname: Jo
authors.forename: Khalid
authors.initials: K
authors.lastname: Chakir
authors.forename: Victor
authors.initials: V
authors.lastname: Maltsev
authors.forename: Ming
authors.initials: M
authors.lastname: Zheng
authors.forename: Michael T
authors.initials: MT
authors.lastname: Crow
authors.forename: Wang
authors.initials: W
authors.lastname: Wang
authors.forename: Edward G
authors.initials: EG
authors.lastname: Lakatta
authors.forename: Rui-Ping
authors.initials: RP
authors.lastname: Xiao
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002478:Cells, Cultured / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors / Q000502:physiology; D044387:GTP-Binding Protein beta Subunits / Q000502:physiology; D044388:GTP-Binding Protein gamma Subunits / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D037342:Pertussis Toxin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D011224:Prazosin / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D018342:Receptors, Adrenergic, beta-1 / Q000502:physiology; D011994:Recombinant Proteins / Q000494:pharmacology; D015290:Second Messenger Systems / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002118:Calcium; D020746:Calcium Channels, L-Type; D002867:Chromones; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D007334:Insulin-Like Growth Factor I; D007545:Isoproterenol; D009025:Morpholines; D009638:Norepinephrine; D010446:Peptide Fragments; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011224:Prazosin; D011412:Propanolamines; D018342:Receptors, Adrenergic, beta-1; D011994:Recombinant Proteins; D000077191:Wortmannin; C118981:G-protein Beta gamma; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C026777:ICI 118551; C114043:BARKct protein, recombinant