Cyclic nucleotide phosphodiesterase (PDE3 and PDE4) limit inotropy and cAMP production induced by the β2-adrenoceptors (β2-AR), salbutamol, in rat ventricular myocardium

Carmen Gonzalez-Muñoz, Teodomiro Fuente, Borja Cordero-Arias, Jesús Hernández-Cascales
University of Murcia, Murcia, Spain

We studied the effects of the non selective PDE inhibitor IBMX, as well as the inhibitors of PDE3 (cilostamide) and PDE4 (rolipram) on contractility and cAMP tissue levels induced by the β2-AR agonist salbutamol (SAL) in rat right ventricle. The role of Gi, in regulating inotropic response to SAL was also evaluated. Sprague-Dawley rats (230-250g) were used. Cumulative concentration-response curves were constructed in right ventricular strips (in Tyrode Solution at 37°C, pH 7.4, and electrically driven at 1 Hz, 1 ms), for SAL alone and in the presence of CGP 20712A (0.3μM) and ICI 118551 (50nM), antagonists of β1- and β2-AR, respectively as well as IBMX (30μM) and cilostamide (0.3μM) or rolipram (1μM). Some animals were treated with Pertussis toxin (PTX, 30μg/Kg. ip.). cAMP levels were determined by immunoassay. Data presented as mean ± s.e.m (n) and analysed by Students t-test or ANOVA. CGP 20712A abolished the inotropic effect of SAL (0.1μM −1mM), which was restored by either IBMX (Emax= 43.6±7.5%;-log EC50=6.2±0.03;n=5) or rolipram+cilostamide (Emax=24.6±5.4%,n=4). These effects were virtually abolished by ICI 118551. SAL, in the presence of CGP 20712A, increases contractility by 9.1±1%, n=4, P<0.05) in rats pretreated with PTX. IBMX enhances by ≈150%, cAMP production induced by SAL (0.5μM) in the presence of CGP 20712A and this effect was abolished by ICI 118551. Also, rolipram combined with cilostamide increases by ≈60% cAMP levels caused by SAL+CGP 20712A. This study has demonstrated that both, PDE3 and PDE4, limit contractile responses and cAMP production induced by β2-AR activation in rat ventricular myocardium. PDEs are more important than Gi proteins in blunting inotropic effect mediated by β2-AR in this tissue. Supported by grant 05/2338 from the “Ministerio de Sanidad y Consumo” (Spain).