The tyrosine kinase inhibitor genistein inhibits mu‐opioid mediated adenylyl cyclase sensitization in C6 cells expressing a mu‐opioid receptor

Abstract

Acute mu‐opioid treatment of cells leads to inhibition of adenylyl cyclase through Gi/o proteins. Opioid withdrawal is characterized by adenylyl cyclase sensitization and cAMP overshoot, an increase in forskolin‐stimulated cAMP accumulation upon removal of chronic agonist. Kinase enzymes have been implicated in the development of sensitization. Kinase inhibitors with specificity for different enzymes were evaluated for their ability to inhibit sensitization following chronic opioid exposure in C6 rat glioma cells expressing the mu‐receptor (C6mu). Notably, treatment with the tyrosine kinase inhibitor genistein (100 μM) caused a 5‐fold rightward shift in the ability of DAMGO to induce adenylyl cyclase sensitization following 1 h agonist treatment. This effect was surmountable at high concentrations of DAMGO suggesting alternative pathway(s); however, the ability of genistein to inhibit sensitization was not significantly enhanced by combinations of kinase inhibitors. Genistein did not significantly alter basal cAMP levels, acute DAMGO‐mediated inhibition of forskolin‐stimulated cAMP production, or the development of tolerance. Results show that the development of adenylyl cyclase sensitization in C6mu cells is mediated in part by phosphorylation by tyrosine kinase enzymes but alternative unidentified pathways are available in the presence of genistein. Supported by DA04087 and DA19276.