The role of phosphodiesterase in mediating the effect of protein kinase C on cyclic AMP accumulation upon κ-opioid receptor stimulation in the rat heart

This study determined whether phosphodiesterase (PDE) was activated by protein kinase C (PKC) upon kappa-receptor stimulation, and if so, to identify the isozyme. We first studied the effects of trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulphonate (U50,488H), a selective kappa-opioid receptor (OR) agonist, and phorbol-12-myristate-13-acetate (PMA), a PKC activator, on cAMP accumulation and PDE activity in rat ventricular myocytes when PKC and PDE were inhibited by respective inhibitors. Like PMA, U50,488H decreased the forskolin-stimulated cAMP accumulation and dose-dependently stimulated the PDE activity, which were antagonized by 10(-6) M chelerythrine and bisindolylmaleimide I, selective PKC antagonists. In addition, 3-isobutyl-1-methylxanthine, a PDE inhibitor, dose-dependently attenuated the inhibition on forskolin-stimulated cAMP accumulation and abolished the stimulation on PDE activity by U50,488H and PMA. The observations suggest that PKC may enhance cAMP degradation through activating PDE upon kappa-OR stimulation. To identify the isozyme(s) mediating the effect of PKC upon kappa-OR stimulation, selective inhibitors were used. We found that 10(-5) M Ro-20-1724, a selective cAMP-specific PDE (PDE-IV) inhibitor, abolished the inhibitory effects of U50,488H and PMA, whereas 8-methoxymethyl-3-isobutyl-1-methylxanthine, erythro-9-(2-hydroxy-3-nonyl) adenine, cilostamide, and zaprinast, selective inhibitors of Ca2+/calmodulin-dependent PDE (PDE-I), cGMP-stimulated PDE (PDE-II), cGMP-inhibited PDE (PDE-III), and cGMP-specific PDE (PDE-V), respectively, had no effect. Moreover, rolipram, another selective PDE-IV inhibitor, also dose-dependently attenuated the inhibition on forskolin-stimulated cAMP accumulation and stimulation on PDE activity by U50,488H and PMA. In conclusion, this study has provided evidence for the first time that PKC and PDE-IV mediate the action of kappa-OR.