Evidence for a β2-Adrenergic/Arachidonic Acid Pathway in Ventricular Cardiomyocytes

Abstract

The signaling pathway mediating the contractile effect of ␤ 2 -adrenergic receptors (␤ 2 -AR) in the heart is still matter of debate. By using embryonic chick ventricular cardiomyocytes that express both functional ␤ 1 -and ␤ 2 -ARs, we show here that the specific ␤ 2 -AR agonist, zinterol, increases the amplitude of Ca 2؉ transients and cell contraction of electrically stimulated cells. Zinterol, up to 10 M, did not stimulate adenylyl cyclase activity, and its effect on Ca ␤ 1 -and ␤ 2 -Adrenergic receptors (␤ 1 -and ␤ 2 -ARs) 1 coexist in the hearts of various animal species, including humans. However, their relative amount and their respective participation in the positive chronotropic and inotropic effects of adrenaline and noradrenaline vary depending on the cardiac tissue, the animal species, and/or the pathophysiological state (1, 2). In the non-failing human left ventricle, ␤ 1 -ARs represent 80% of the total ␤-ARs but mediate about 60% only of ␤-adrenergicinduced ventricular contractility (3). In the human failing heart, the ␤ 1 /␤ 2 -AR ratio decreases, and the contribution of ␤ 2 -AR to the contractile responses becomes predominant over that of ␤ 1 -AR, in particular at low adrenaline concentrations (3, 4). For these reasons, the potential role of ␤ 2 -AR for improving cardiac performance has received considerable attention. In fact, the myocardial-targeted overexpression of ␤ 2 -ARs in transgenic mice significantly enhanced myocardial left ventricular contractility (5).It is well documented that ␤ 1 -AR and ␤ 2 -AR subtypes are coupled to adenylyl cyclase activation and that stimulation of both receptors generally leads to an increase in cellular cAMP (4, 6, 7). In human healthy heart, ␤ 2 -ARs are more efficiently coupled to adenylyl cyclase than ␤ 1 -ARs (6 -10). However, during cardiac failure, ␤ 2 -AR subtypes are partially uncoupled from adenylyl cyclase (6, 7), whereas their contribution to the positive inotropic effects of adrenaline and noradrenaline is increased to 63% (7). In addition, 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.Angiotensin II (14,15), bradykinin (16,17), and endothelin (15, 18), which exert positive inotropic responses, evoke AA release in heart. Furthermore, in a recent study, we have demonstrated that glucagon action relies not only on cAMP but also on the synergistic support of AA, by activation of the cPLA 2 which hydrolyzes the sn-2 fatty acyl ester bonds of membranous phospholipids (15).The aim of the present study was to investigate the respective role of cAMP and AA in the cardiac response to ␤-adrenergic agonists. We used the model of embryonic chick ventricular cardiomyocytes that has been widely exploited ...

β2-Adrenergic Receptor Agonists Increase Intracellular Free Ca2+ Concentration Cycling in Ventricular Cardiomyocytes through p38 and p42/44 MAPK-mediated Cytosolic Phospholipase A2 Activation

“…We demonstrate a dose-dependent redistribution of cPLA 2 activity from the cytosol to membranes in response to low concentrations of zinterol, with the maximal effect being observed at 30 nM zinterol. This dose dependence correlates with our previous data on zinterol-induced AA release (5). At such doses, zinterol is unequivocally known to act through ␤ 2 -AR.…”

“…Cells were then washed two times with saline buffer B and allowed to incubate in the same buffer for 15 min at 25°C to facilitate hydrolysis of intracellular Fura-2/AM. The concentration of Fura-2 in myocytes was estimated as described previously (5,6,21,22) according to the procedure of Donnadieu et al (23). Under usual loading conditions, the average intracellular concentration of Fura-2 was 15 M. Ca 2ϩ imaging was essentially performed as described by Sauvadet et al (6,21).…”

“…Primary monolayer cultured heart cells were prepared from 13-day-old embryonic chick ventricles as previously described (5,6,21,22). Briefly, cells were dissociated by repeated cycles of trypsinization.…”

“…However, the role of cAMP in the functional response to ␤ 2 -AR stimulation is controversial, and there is accumulating evidence that ␤ 2 -AR agonists could modulate cardiac excitation-contraction coupling via a cAMPindependent mechanism (1). We have recently identified an alternative pathway relaying the positive inotropic effect of ␤ 2 -AR agonists in embryonic chick heart cells (5). In these cells, stimulation of ␤ 2 -ARs triggers the production of arachidonic acid (AA) via a pertussis toxin-sensitive G protein pathway.…”

Arachidonic acid incorporation and turnover is decreased in sympathetically denervated rat heart

“…Thrombin stimulates choline plasmalogen (PlsCho) turnover via the plasmalogen-selective iPLA 2 to release 20:4 n-6 and lysoPlsCho, both of which are potent second messengers (32). ␤ 2 -Adrenergic receptor stimulation also leads to 20:4 n-6 release through activation of a PLA 2 in the cytosol (37), which suggests a role for 20:4 n-6 in regulating heart ionotropic and chronotropic events (45).…”