MOBILIZATION OF CA2+ FROM INTRACELLULAR STORES IN TRANSFECTED NEURO(2A) CELLS BY ACTIVATION OF MULTIPLE OPIOID RECEPTOR SUBTYPES

In neuronal cell lines, activation of opioid receptors has been shown to mobilize intracellular Ca2+ stores. In this report, we describe the excitatory actions of opioid agonists on murine neuroblastoma neuro(2 a) cells stably expressing either delta, mu, or kappa opioid receptors . Fura-2-based digital imaging was used to record opioid-induced incre ases in intracellular Ca2+ concentration ([Ca2+](i)). Repeated challen ges of delta, mu, or kappa opioid receptor expressing cells with 100 n M [D-Ala(2),D-Leu(5)]-enkephalin (DADLE), [D-Ala(2),N-Me-Phe(4),Gly-ol ]-enkephalin (DAMGO), or trans-(+/-)-3,4-dichloro N-methyl-N-(2-[1-pyr ollidinyl] cyclohexyl) benzene acetamide (U-50488H), respectively, eli cited reproducible Ca2+ responses. Non-transfected neuro(2a) cells did not respond to opioid agonists. Removal of extracellular Ca2+ from th e hath Frier to and during agonist challenge ,a did not affect signifi cantly the agonist-evoked increase in [Ca2+](i), indicating that the r esponse resulted from the release of Ca2+ from intracellular stores. N aloxone reversibly inhibited responses in all three cell lines, confir ming that they were mediated by opioid receptors. Expression oi cloned opioid receptors in neuro(2a) cells, coupled with digital [Ca2+](i) i maging, provides a model system fur the study of opioid receptors and opioid-activated signaling processes. The fact that all three receptor s coupled to the same intracellular signaling mechanism suggests that the primary functional difference between opioid responses in vivo res ults from their selective localization. (C) 1997 Elsevier Science Inc.