Role of nitric oxide/cyclic GMP and cyclic AMP in β3 adrenoceptor-chronotropic response

Abstract

In this study we determine different signaling pathways involved in â3 adrenoceptor- (â3-AR) dependent frequency stimulation in isolated rodent atria. Promiscuous coupling between different G-proteins and â3-AR could explain the multiple functional effects of â3-AR stimulation. We examine the mechanisms and functional consequences of dual adenylate cyclase and guanylate cyclase pathways coupling to â3-AR in isolated rodent atria. The â3-AR selective agonists ZD 7114 and ICI 215001 stimulated in a dose-dependent manner the contraction frequency that significantly correlated with cyclic AMP (cAMP) accumulation. Inhibition of adenylate cyclase shifted the chronotropic effect to the right. On the other hand, the ZD 7114 activity on frequency was enhanced by the inhibition of nitric oxide synthase (NOS) and soluble guanylate cyclase. This countervailing negative chronotropic nitric oxide-cyclic GMP (NO-cGMP) significantly correlated with the increase on NOS activity and cGMP accumulation. Current analysis showed a negative cross-talk between cAMP chronotropic and NO-cGMP effects by inhibition of phospholipase C (PLC), calcium/calmodulin (CaM), protein kinase C (PKC), NOS isoforms and Gi-protein on the effects of â3-AR stimulation. RT-PCR detected both eNOS and nNOS in isolated rat atria. NOS isoforms performed independently. Only nNOS participated in limiting the effect of â3-AR stimulation. In eNOS-KO (eNOS-/-) mice the chronotropic effect of â3-AR agonists did not differ from wild type (WT) mice atria, but it was increased by the inhibition of nNOS activity. Our results suggest that the increase in frequency by â3-AR activation on isolated rodent atria is associated to a parallel increases in cAMP. The nNOS-cGMP pathway negatively modulates â3-AR activation. Multiple signal transduction pathways between G-protein and â3-AR may protect myocardium from catecholamine-induced cardiotoxic effects.