Methadone increases intracellular calcium in SH-SY5Y and SH-EP1-hα7 cells by activating neuronal nicotinic acetylcholine receptors

Abstract

(-)-Methadone acts as an agonist at opioid receptors. Both (+)- and (-)-enantiomers of methadone have been suggested to be potent non-competitive antagonists of α3β4 neuronal nicotinic acetylcholine receptors (nAChRs). In the present study, we have examined interactions of methadone with nAChRs by using receptor binding assays, patch-clamp recording and calcium fluorometry imaging with SH-SY5Y cells naturally expressing α7 and α3* nAChR subtypes and SH-EP1-hα7 cells heterologously expressing human α7 nAChRs. Methadone potently inhibited binding of [ 3H]methyl-lycaconitine to α7 nAChRs and that of [ 3H]epibatidine to α3* nAChRs. Methadone pretreatment induced up-regulation of epibatidine binding sites in SH-SY5Y cells. Using whole-cell patch-clamp recording, both isomers of methadone activated cation currents via mecamylamine-sensitive nAChRs in SH-SY5Y cells. Nicotine and both (+)- and (-)-methadone evoked increases in [Ca2+]i in both fluo-3AM loaded cell lines, and these effects were blocked by mecamylamine and by the α7 selective antagonist methyllycaconitine, suggesting effects of methadone as α7-nAChR agonist. Sensitivity of sustained nicotine and methadone effects to blockade by CdCl2, ryanodine and xestospongin-c implicates voltage-operated Ca2+ channels and intracellular Ca 2+ stores as downstream modulators of elevated [Ca2+] i. Collectively, our results suggest that methadone engages in complex and potentially pharmacologically significant interactions with nAChRs. © 2005 International Society for Neurochemistry.