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

In this study we determine different signaling pathways involved in β3 adrenoceptor (β3-AR) dependent frequency stimulation in isolated rodent atria. Promiscuous coupling between different G-proteins and β3-AR could explain the multiple functional effects of β3-AR stimulation. We examine the mechanisms and functional consequences of dual adenylate cyclase and guanylate cyclase pathways coupling to β3-AR in isolated rodent atria. The β3-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 β3-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 β3-AR stimulation. In eNOS-KO (eNOS–/–) mice the chronotropic effect of β3-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 β3-AR activation on isolated rodent atria is associated to a parallel increases in cAMP. The nNOS-cGMP pathway negatively modulates β3-AR activation. Multiple signal transduction pathways between G-protein and β3-AR may protect myocardium from catecholamine-induced cardiotoxic effects.