Evidence for a beta2-adrenergic/arachidonic acid pathway in ventricular cardiomyocytes. Regulation by the beta1-adrenergic/camp pathway.
The signaling pathway mediating the contractile effect of beta2-adrenergic receptors (beta2-AR) in the heart is still matter of debate. By using embryonic chick ventricular cardiomyocytes that express both functional beta1-and beta2-ARs, we show here that the specific beta2-AR agonist, zinterol, increases the amplitude of Ca2+ transients and cell contraction of electrically stimulated cells. Zinterol, up to 10 microM, did not stimulate adenylyl cyclase activity, and its effect on Ca2+ transients was unmodified by the specific cAMP antagonist, (Rp)-cAMPS. In contrast, zinterol (10-100 nM) triggered arachidonic acid (AA) release from [3H]AA-loaded cells via the activation of the cytosolic phospholipase A2 (cPLA2). Stimulation of the Ca2+ transients by zinterol was abolished by the cPLA2 inhibitor, AACOCF3, and was mimicked by AA (0.3-3 microM). Both stimulations of [3H]AA release and of [Ca2+]i cycling by zinterol were abolished after treatment of the cardiomyocytes with pertussis toxin. Although cell responses to beta2-AR stimulation were mediated by AA, they were under cAMP control as follows: (i) the beta1-AR stimulation exerted a cAMP-mediated negative constraint on the beta2-AR/cPLA2 pathway; (ii) cAMP potentiated AA action downstream beta-AR stimulation. We conclude that, in cardiomyocytes, beta2-AR is coupled to cPLA2 activation via a pertussis toxin-sensitive G protein. These results demonstrate the involvement of the cPLA2/AA pathway in mediating positive inotropic effects, which could potentially compensate for a defective cAMP pathway.
Pavoine
C
C
INSERM Unité 99, Hôpital Henri Mondor, 94010 Créteil, France. pavoine@im3.inserm.fr
Magne
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S
Sauvadet
A
A
Pecker
F
F
D000262:Adenylyl Cyclases / Q000378:metabolism; D058666:Adrenergic beta-2 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D000242:Cyclic AMP / Q000378:metabolism; D004558:Electric Stimulation; D004789:Enzyme Activation; D004983:Ethanolamines / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D016276:Ventricular Function
D058666:Adrenergic beta-2 Receptor Agonists; D000318:Adrenergic beta-Agonists; D004983:Ethanolamines; D018343:Receptors, Adrenergic, beta-2; D016718:Arachidonic Acid; C002904:zinterol; D000242:Cyclic AMP; D010741:Phospholipases A; D054467:Phospholipases A2; D000262:Adenylyl Cyclases