Interaction among mu-opioid receptors and alpha 2-adrenoceptors on SH-SY5Y human neuroblastoma cells.
The clonal human neuroblastoma cell line SK-N-SH-SY5Y was previously shown to express mu-opioid and alpha 2-adrenoceptors which are both negatively coupled to adenylyl cyclase. Because of the potential use of alpha 2-agonists in the treatment of narcotic dependence, we tested the interactions among he alpha 2-agonists, clonidine and norepinephrine, and morphine on AC in SH-SY5Y cells. Pretreatment with retinoic acid resulting in partial neuronal differentiation greatly enhanced the cells' sensitivity towards adenylyl cyclase stimulation by prostaglandin E1, and its inhibition by morphine and alpha 2-agonists. Norepinephrine (EC50 = 69 nM) maximally inhibited prostaglandin E1-stimulated cAMP accumulation (by approximately 83%), and the alpha 2-agonist yohimbine reversed these effects. Clonidine (EC50 = 32 nM) was a partial agonist, with 50 to 60% maximal inhibition. The combined effects of morphine (maximum approximately 70% inhibition) and norepinephrine exceeded the effect of either agent alone, yielding more than 90% inhibition of prostaglandin E1-stimulated cAMP accumulation. As previously reported for morphine, only a partial tolerance was observed for adenylyl cyclase inhibition by norepinephrine. Further, no cross-tolerance was observed between clonidine and morphine. The combined results indicate that mu-opioid receptors and an alpha 2-adrenoceptor subtype are colocalized on the same cells in SH-SY5Y culture, which hence serves as a model to study opioid-alpha 2-adrenergic interactions.
Department of Pharmacy, University of California, San Francisco 94143.
J
J
Lameh
S
S
Eiger
W
W
Sadée
D000067956:Adenylyl Cyclase Inhibitors; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000242:Cyclic AMP / Q000032:analysis; D004347:Drug Interactions; D004361:Drug Tolerance; D006801:Humans; D009020:Morphine / Q000494:pharmacology; D009447:Neuroblastoma; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D017450:Receptors, Opioid, mu / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D000067956:Adenylyl Cyclase Inhibitors; D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D017450:Receptors, Opioid, mu; D009020:Morphine; D000242:Cyclic AMP