Vol. 292, Issue 3, 1065-1070, March 2000

The Role of Phosphodiesterase in Mediating the Effect of Protein Kinase C on Cyclic AMP Accumulation upon -Opioid Receptor Stimulation in the Rat Heart¹

Jin-Song Bian, Wei-Min Zhang, Jian-Ming Pei and Tak-Ming Wong

Department of Physiology and Institute of Cardiovascular Science and Medicine, Faculty of Medicine, The University of Hong Kong, Hong Kong, China

This study determined whether phosphodiesterase (PDE) was activated by protein kinase C (PKC) upon -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 -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 10⁶ 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 -OR stimulation. To identify the isozyme(s) mediating the effect of PKC upon -OR stimulation, selective inhibitors were used. We found that 10⁵ 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 -OR.