CHARACTERIZATION OF BIOCHEMICAL EFFECTS OF CGS 21680C, AN A(2)-ADENOSINE RECEPTOR AGONIST, IN THE MAMMALIAN VENTRICLE

Effects of a putative A(2)-adenosine receptor agonist 2-[(p-2-carboxye thyl)-phenethylamino] boxamide-adenosine (CGS 21680C) on force of cont raction, protein phosphorylation, cyclic adenosine monophosphate (cAMP ) content, and the activity of phosphodiesterase (PDE) isoenzymes in g uinea pig ventricular (GPV) preparations were studied. CGS 21680C (1-1 00 mu M) did not affect force of contraction in isolated electrically driven papillary muscles and was ineffective in increasing phosphoryla tion of phospholamban (PLB) and the inhibitory subunit of troponin (Tn I) in [P-32]-labeled GPV cardiomyocytes.; However, under the same cond itions, CGS 21680C (10 mu M) increased cAMP content from 4.3 +/- 0.2 t o 13.0 +/- 0.6 pmol/mg:: protein, and this effect was completely aboli shed by Az-adenosine receptor antagonist 6-dihydro-1,2,4-triazolo-(1,5 -c)quinazolin-5-imine (CGS 15943A). CGS 21680C (10 mu M) inhibited PDE isoenzymes I, II, III, IV by 7.0, 8.3, 4.7, and 23.2%, respectively. Similarly, rolipram (100 mu M), a selective PDE IV inhibitor, increase d cAMP content from 4.4 +/- 0.3 to 7.2 +/- 0.3 pmol/mg protein without affecting the phosphorylation state of PLB and TnI. We conclude that CGS 21680C increases cAMP content in GPV cardiomyocytes by activation of adenylyl cyclase or in part by inhibition of PDE IV activity. The i ncrease in cAMP content by CGS 21680C or rolipram is ineffective in in creasing phosphorylation of PLB and TnI. These results support the con cept of compartments for cAMP or protein kinase, A or both in cardiomy ocytes that are not coupled to phosphorylation and contractility.