Evidence for a β2-Adrenergic/Arachidonic Acid Pathway in Ventricular Cardiomyocytes: REGULATION BY THE β1-ADRENERGIC/cAMP PATHWAY

Catherine Pavoine,Sandrine Magne,Anne Sauvadet,Françoise Pecker

doi:10.1074/jbc.274.2.628

Abstract

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.

Highlights

␤1- and ␤2-Adrenergic receptors (␤1- and ␤2-ARs)1 coexist in the hearts of various animal species, including humans
Cell responses to ␤2-AR stimulation were mediated by arachidonic acid (AA), they were under cAMP control as follows: (i) the ␤1-AR stimulation exerted a cAMP-mediated negative constraint on the ␤2-AR/cytosolic phospholipase A2 (cPLA2) pathway; (ii) cAMP potentiated AA action downstream ␤-AR stimulation
We show that ␤1- and ␤2-ARs are both expressed in embryonic chick ventricular cardiomyocytes, and this model allowed us to demonstrate the following: (i) ␤2-ARs are coupled to cPLA2 via a Gi protein; (ii) cAMP exerts a dual tuning on cell responses to ␤2-AR stimulation

Summary

Introduction

␤1- and ␤2-Adrenergic receptors (␤1- and ␤2-ARs) coexist in the hearts of various animal species, including humans. Studies in the rat heart [11, 12] and in the non-failing and failing canine heart [13] have demonstrated a dissociation between the inotropic effect of ␤2-AR and cellular cAMP increase Based on those observations, Xiao et al [12] proposed that unidentified signal transduction pathway(s), other than adenylyl cyclase and cAMP, could be involved in the cardiac inotropic response to ␤2-AR stimulation. We used the model of embryonic chick ventricular cardiomyocytes that has been widely exploited for studies on metabolism, contractile physiology, electrophysiology, and examination of pathophysiologic states such as ischemia [19] We show that those cells, in addition to expressing ␤1-AR [19, 20], respond to ␤2-AR stimulation. Cell responses to ␤2-AR stimulation were mediated by AA but under cAMP control

Objectives

Methods

Findings

Conclusion