Tolerance to morphine at the mu-opioid receptor differentially induced by cAMP-dependent protein kinase activation and morphine.
Human neuroblastoma SH-SY5Y cells express endogenous mu-opioid receptor and develop cellular tolerance to morphine after prolonged (>/=4 h) treatment with morphine. Treatment with forskolin (25 microM, 12 h), an adenylyl cyclase activator, also desensitized mu-opioid receptor response to morphine (10 microM) by 38% (P<0. 001), which was reversed by the cyclic AMP (cAMP) dependent kinase inhibitor N-(2-aminoethyl)-5-isoquinolinesulfonamide (H8) (100 microM). Treatment with both morphine and forskolin appeared to cause an additive effect in desensitizing mu-opioid receptor. In mu-opioid receptor stably transfected human embryonic kidney 293 (HEK-mu) cells, morphine treatment produced cAMP upregulation, yet failed to induce mu-opioid receptor tolerance. However, treatment with forskolin (25 microM) or 8-bromo-cAMP (1mM) led to profound mu-opioid receptor tolerance, which was reversed by H8. These results demonstrate that cAMP-dependent kinase activation causes mu-opioid receptor tolerance. However, morphine-induced mu-opioid receptor tolerance in SH-SY5Y cells is not mediated by cAMP-dependent kinase activation. In addition, our results indicate that cAMP-upregulation does not necessarily lead to mu-opioid receptor tolerance.
Wang
Z
Z
Department of Pharmaceutical Chemistry, University of California, San Francisco, CA, USA. zwang@u.arizona.edu
Sadée
W
W
D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004361:Drug Tolerance; D004789:Enzyme Activation; D006801:Humans; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D010766:Phosphorylation; D017450:Receptors, Opioid, mu / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D009294:Narcotics; D017450:Receptors, Opioid, mu; D005576:Colforsin; D009020:Morphine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases