EFFECTS OF ADENOSINE RECEPTOR AND MUSCARINIC CHOLINERGIC RECEPTOR AGONISTS ON CARDIAC PROTEIN-PHOSPHORYLATION - INFLUENCE OF PERTUSSIS TOXIN

In isolated P-32-labeled guinea pig ventricular cardiomyocytes phospholamban (PLB), myosin light chain 2 and the inhibitory subunit of troponin (Tnl) were identified by antibodies, in isolated P-32-labeled guinea pig ventricular cardiomyocytes isoproterenol (0.1 mu mol/l) increased phosphorylation of PLB and of the inhibitory subunit of Tnl to 159 and 119% of control, respectively, without effect on the phosphorylation state of myosin light chain 2. Additionally applied carbachol or (-)-N-6-phenylisopropyl adenosine reduced phosphorylation of PLB and Tnl without reducing cyclic AMP content. After pretreatment of guinea pigs with pertussis toxin (18 mu g/100 g b.wt.), carbachol or (-)-N-6-phenylisopropyladenosine failed to reduce isoproterenol-stimulated phosphorylation of both PLB and Tnl. It is concluded that the reductions by carbachol and (-)-N-6-phenylisopropyladenosine of isoproterenol-stimulated PLB phosphorylation and Tnl phosphorylation are pertussis toxin-sensitive.