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.
Publication types
-
Research Support, Non-U.S. Gov't
-
Research Support, U.S. Gov't, P.H.S.
MeSH terms
-
Androstadienes / pharmacology
-
Animals
-
Calcium / metabolism*
-
Calcium Channels, L-Type / metabolism*
-
Calcium Signaling / physiology
-
Cells, Cultured / drug effects
-
Cells, Cultured / enzymology
-
Cells, Cultured / metabolism
-
Chromones / pharmacology
-
Colforsin / pharmacology
-
Cyclic AMP / antagonists & inhibitors*
-
Cyclic AMP / pharmacology
-
Cyclic AMP-Dependent Protein Kinases / pharmacology
-
Cyclic AMP-Dependent Protein Kinases / physiology*
-
Enzyme Activation / drug effects
-
GTP-Binding Protein alpha Subunits, Gi-Go / antagonists & inhibitors
-
GTP-Binding Protein alpha Subunits, Gi-Go / physiology
-
GTP-Binding Protein beta Subunits / physiology
-
GTP-Binding Protein gamma Subunits / physiology
-
Insulin-Like Growth Factor I / pharmacology
-
Ion Transport / drug effects
-
Isoproterenol / pharmacology
-
Morpholines / pharmacology
-
Myocardial Contraction
-
Myocytes, Cardiac / drug effects
-
Myocytes, Cardiac / enzymology*
-
Myocytes, Cardiac / metabolism
-
Norepinephrine / pharmacology
-
Patch-Clamp Techniques
-
Peptide Fragments / pharmacology
-
Pertussis Toxin / pharmacology
-
Phosphatidylinositol 3-Kinases / physiology*
-
Phosphoinositide-3 Kinase Inhibitors
-
Phosphorylation / drug effects
-
Prazosin / pharmacology
-
Propanolamines / pharmacology
-
Protein Processing, Post-Translational / drug effects
-
Rats
-
Receptors, Adrenergic, beta-1 / physiology
-
Recombinant Proteins / pharmacology
-
Second Messenger Systems / physiology*
-
Signal Transduction / physiology*
-
Wortmannin
Substances
-
Androstadienes
-
Calcium Channels, L-Type
-
Chromones
-
G-protein Beta gamma
-
GTP-Binding Protein beta Subunits
-
GTP-Binding Protein gamma Subunits
-
Morpholines
-
Peptide Fragments
-
Phosphoinositide-3 Kinase Inhibitors
-
Propanolamines
-
Receptors, Adrenergic, beta-1
-
Recombinant Proteins
-
Colforsin
-
2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
-
ICI 118551
-
Insulin-Like Growth Factor I
-
Cyclic AMP
-
Pertussis Toxin
-
Cyclic AMP-Dependent Protein Kinases
-
BARKct protein, recombinant
-
GTP-Binding Protein alpha Subunits, Gi-Go
-
Isoproterenol
-
Calcium
-
Norepinephrine
-
Prazosin
-
Wortmannin