Influence of opioids on β-receptors down-regulation: studies in cultured C6 glioma cells

Evidence for κ‐ and μ‐Opioid Receptor Expression in C6 Glioma Cells

“…To determine whether the treatment of C6 cells with DM1 had induced an increase in K-or j.t-opioid receptor message, semiquantitative analysis of PCR amplification was performed by incorporating GAPDH primer pairs in the reaction. In previous experiments, it was noted that [ 3H1-dihydromorphine binding was detectable after 2-h DM1 treatment and peaked after 10-20 h (Reggiani et al, 1987). With this in mind, time course experiments were performed in which receptor expression was compared after 0, 0.5, 1, 1.5, 2, and 20 h of DM1 treatment.…”

“…The astrocytoma cell line rat C6 glioma, when treated with desipramine (DM1), has been used as a model system to study opioid effects on cell proliferation (Barg et al, 1991(Barg et al, , 1994a as well as opioid inhibition of adenylate cyclase activity (Reggiani et al, 1987), Ca2m obilization, phosphatidylinositide turnover, and DNA synthesis (Barg et al, 1994a,b). In these previous studies, naive C6 cells appeared to possess little if any opioid binding and displayed no detectable opioid receptormediated functions.…”

“…The ti-selective ligands [3H1-dihydromorphine and [3H1 morphine demonstrated low affinity for the opioid receptor populations in DM1-treated C6 cells. KD values ranging from 14 to 60 nM were reported for the two ligands (Albouz et al, 1982;Reggiani et al, 1987;Barg et al, 1991;Dobrenis et al, 1995 (Albouz et al, 1982;Reggiani et al, 1987;Barg et al, 1991). However, the endogenous opioid peptide /3-endorphin, in the presence of protease inhibitors, displayed high affinity (IC 50 4-6 nM) for these sites in heterologous binding assays (Reggiani et al, 1986;Barg et al, 1991).…”

Opioids inhibit endothelin-mediated DNA synthesis, phosphoinositide turnover, and Ca2+ mobilization in rat C6 glioma cells

“…The DMI-induced C6 glioma opioid receptor binds P-endorphin, morphine, etorphine, naloxone, as well as the anti-idiotypic antibody Ab2AOR, which has been shown to have opioid agonist activity (Coscia et al, 199 1;Barg et al, 1993b). The DMI-induced opioid binding sites are functional and morphine inhibits both isoproterenol-stimulated and basal CAMP levels in the cells (Tocque et al, 1984;Reggiani et al, 1987). have recently demonstrated that opioid agonists reduce the cell number and thymidine labeling of a specific type of "flat" (type 1) neonatal mouse brain astrocyte.…”

“…In addition, the rat C6 glioma cell line has proven to be a useful model for investigating the properties of opioid receptors on glial cells. Although C6 cells do not display opioid binding under standard tissue culture conditions, they express opioid receptors in the presence of the tricyclic antidepressant drug DMI (Albouz et al, 1982;Tocque et al, 1984;Reggiani et al, 1987). The DMI-induced C6 glioma opioid receptor binds P-endorphin, morphine, etorphine, naloxone, as well as the anti-idiotypic antibody Ab2AOR, which has been shown to have opioid agonist activity (Coscia et al, 199 1;Barg et al, 1993b).…”