FUNCTIONAL COUPLING OF THE DELTA-OPIOID, MU-OPIOID, AND KAPPA-OPIOID RECEPTORS TO MITOGEN-ACTIVATED PROTEIN-KINASE AND ARACHIDONATE RELEASEIN CHINESE-HAMSTER OVARY CELLS

To examine whether the mitogen-activated protein kinase (MAPK) cascade and phospholipase A(2) (PLA(2)) are involved in the signal transducti on mechanism of the opioid receptor, the delta-, mu-, and kappa-opioid receptors were stably expressed from cDNA in Chinese hamster ovary ce lls. Activation of the delta-, mu-, and kappa-receptors by agonists in duced a rapid and transient increase in MAPK activity accompanied by r educed electrophoretic mobility of the 42-kDa isoform of MAPK (p42), p robably owing to phosphorylation. The opioid receptor-mediated increas e in MAPK activity was suppressed not only by pretreatment with genist ein, a tyrosine protein kinase inhibitor, but also by prolonged exposu re to phorbol 12-myristate 13-acetate and pretreatment with GF 109203X , a selective protein kinase C (PKC) inhibitor, suggesting the involve ment of PKC as well as tyrosine protein kinase, Furthermore, stimulati on of the delta-, mu-, and kappa-receptors with opioid agonists in the presence of A23187, a calcium ionophore, resulted in an increase in a rachidonate release, suggesting that PLA(2) is activated by the opioid receptors when the intracellular Ca2+ concentration is elevated. Both MAPK activation and increase in arachidonate release mediated by the opioid receptors were abolished by pretreatment with pertussis toxin, suggesting that these responses are mediated by G(i) or G(o) types of GTP-binding regulatory proteins.