Adenosine receptor coupling to adenylate cyclase of rat ventricular myocyte membranes

Abstract

The effects of adenosine analogues on beta-adrenergic receptor and receptor-independent elicited increases in adenylate cyclase activity were investigated using membranes obtained from primary cultures of adult rat ventricular myocytes. Phenylisopropyladenosine, an A1-receptor agonist, at concentrations of 0.1, 1.0, and 10 microM, maximally inhibited isoproterenol-stimulated adenylate cyclase activity by 35, 55, and 41%, respectively. The inhibition by phenylisopropyladenosine was antagonized by 10 microM theophylline. One micromolar phenylisopropyladenosine was much less effective at attenuating forskolin-stimulated activity, such that the maximum inhibition was 26%. Phenylisopropyladenosine had no effect on adenylate cyclase stimulation by 5'-guanylylimidodiphosphate. Phenylaminoadenosine, an A2 agonist, at 10 microM or greater stimulated adenylate cyclase activity. This effect was not significantly inhibited by theophylline or 0.1 microM 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), which antagonized phenylisopropyladenosine inhibition of isoproterenol-stimulated adenylate cyclase activity. Additionally, N-ethylcarboxamidoadenosine, a nonselective adenosine-receptor agonist, had no effect on adenylate cyclase activity in the absence of DPCPX but stimulated adenylate cyclase activity in the presence of DPCPX. These results indicate that both A1 and A2 receptors exist on the ventricular myocyte sarcolemma. More importantly, the findings suggest that adenosine inhibition of catecholamine-stimulated adenylate cyclase activity is primarily due to an alteration in beta-adrenergic receptor-mediated transduction and perhaps in part by a direct inhibition of the catalytic component.

Evidence for a cooperation between adenosine A2 receptors and β1‐adrenoceptors on cardiac automaticity in the isolated right ventricle of the rat

“…This agrees with previous results on ventricular automaticity in which NECA was shown to be more potent than CADO, with R-PIA being ineffective, and in relation to the inhibitory effect, R-PIA was about equipotent with CADO, both being more potent than NECA (Hernandez et al, 1989). It has been suggested (Xu et al, 1992) Romano et al (1989), found that NECA in the same concentrations (0.1-10 IIM) as those used in the present work, stimulates adenylate cyclase activity in the rat yentricular myocyte membranes (a typical A2 adenosine effect), only when the Al receptor is blocked with DPCPX.…”

“…To this purpose we studied the effect of NECA, a compound that in rat ventricular myocyte membranes exhibits a typical A2 agonist effect by stimulating adenylate cyclase activity in the presence of the adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (see Romano et al, 1989), which, at low concentrations (5 nM) selectively antagonizes Al adenosine receptors and at high concentrations (10tMm) antagonizes both A1 and A2 adenosine receptors (Bruns et al, 1987;Correia-de-SA ea al., 1991). The subtype of P-adrenoceptor involved in the excitatory effect of NECA was explored by studying the relation between the P agonist isoprenaline and NECA, in the presence of either the Pl antagonists atenolol (Hoffman & Lefkowitz, 1990) or bisoprolol (Wang et al, 1985) and the highly selective P2 antagonist ICI-1 18,551 (Bilski et al, 1983).…”

Pharmacological modifications of the stretch-induced effects on ventricular fibrillation in perfused rabbit hearts

“…Its stimulation augments myocardial contractility, and this response is prevented by adenosine A 2 receptor antagonists. The inotropic response is produced by an increase in adenylyl cyclase and cAMP activity (12,50,53,54) and is similar to the response induced by an increase in extracellular Ca 2ϩ concentration (39,49,52). A cAMP-dependent protein kinase produces hyperphosphorylation of the ryanodine receptor and an increase in spontaneous Ca 2ϩ release from the sarcoplasmic reticulum.…”

“…Finally, in regard to the third substance, the adenosine A 2 receptor has been shown to modulate Ca 2ϩ release from the sarcoplasmic retic-ulum through cAMP-dependent modulation of the ryanodine receptor (20). Adenosine A 2 receptor stimulation produces an increase in adenylyl cyclase activity and cAMP (12,50,53,54), with a positive inotropic response similar to that seen with an increase in extracellular Ca 2ϩ concentrations (49,52), although it is not known whether adenosine A 2 receptor block would modulate the electrophysiological effects of stretch. To clarify the modifications of the electrophysiological effects of stretching under the influence of these three substances, we used an isolated Langendorff-perfused rabbit heart model in which analysis of the dominant frequency (DF) and the activation patterns of VF allowed us to illustrate the electrophysiological modifications produced by acute stretch applied on the free wall of the left ventricle (8,63).…”

Acute adenosinergic cardioprotection in ischemic-reperfused hearts

“…These receptors were thought to primarily exist in vascular and blood cells, where they mediated vasodilatory and anti-inflammatory actions, respectively. However, expression of mRNA encoding the A 2A AR in rat ventricular myocytes (303), together with A 2A AR agonist-me-diated changes in cAMP and contraction of chick (172) and rat myocytes (56, 239,303), support the expression of A 2A ARs on myocytes. This indirect evidence of myocardial expression is supported by a single report of immunological evidence of a canine A 2A AR-like protein in human and porcine ventricular tissue (199).…”