Abstract
This study determined whether phosphodiesterase (PDE) was activated by protein kinase C (PKC) upon κ-receptor stimulation, and if so, to identify the isozyme. We first studied the effects oftrans-(±)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulphonate (U50,488H), a selective κ-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 κ-OR stimulation. To identify the isozyme(s) mediating the effect of PKC upon κ-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 κ-OR.
Footnotes
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Send reprint requests to: T. M. Wong, Ph.D., Department of Physiology, The University of Hong Kong, Li Shu Fan Building, Sassoon Rd., Hong Kong, China. E-mail: wongtakm{at}hkucc.hku.hk
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↵1 This study was supported by a grant from the Research Grant Council, Hong Kong.
- Abbreviations:
- OR
- opioid receptor
- PKC
- protein kinase C
- U50,488H
- trans-(±)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulphonate
- PMA
- phorbol-12-myristate-13-acetate
- PDE
- phosphodiesterase
- PDE-IV
- cAMP-specific PDE
- PDE-I
- Ca2+/calmodulin-dependent PDE
- PDE-II
- cGMP-stimulated PDE
- PDE-III
- cGMP-inhibited PDE
- PDE-V
- cGMP-specific PDE
- BSM
- bisindolylmaleimide I
- MIBMX
- 8-methoxymethyl-3-isobutyl-1-methylxanthine
- EHNA
- erythro-9-(2-hydroxy-3-nonyl) adenine
- DMSO
- dimethyl sulfoxide
- nor-BNI
- nor-binaltorphimine
- AC
- adenylate cyclase
- Received June 22, 1999.
- Accepted November 3, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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