Differential Pharmacological Actions of Methadone and Buprenorphine in Human Embryonic Kidney 293 Cells Coexpressing Human μ-Opioid and Opioid Receptor-Like 1 Receptors

Abstract

Methadone and buprenorphine are used in maintenance therapy for heroin addicts. In this study, we compared their effects on adenylate cyclase (AC) activity in human embryonic kidney (HEK) 293 cells stably overexpressing human μ-opioid receptor (MOR) and nociceptin/opioid receptor-like 1 receptor (ORL1) simultaneously. After acute exposure, methadone inhibited AC activity; however, buprenorphine induced compromised AC inhibition. When naloxone was introduced after 30 min incubation with methadone, the AC activity was enhanced. This was not observed in the case of buprenorphine. Enhancement of the AC activity was more significant when the incubation lasted for 4 h, and prolonged exposure to buprenorphine elevated the AC activity as well. The removal of methadone and buprenorphine by washing also obtained similar AC superactivation as that revealed by naloxone challenge. The study demonstrated that methadone and buprenorphine exert initially different yet eventually convergent adaptive changes of AC activity in cells coexpressing human MOR and ORL1 receptors.

Quantitative study of [Tyr10]nociceptin/orphanin FQ (1-11) at NOP receptors in rat periaqueductal gray and expressed NOP receptors in HEK293 cells

“…However, the results in this study nullify this hypothesis since [Tyr 10 ]N/OFQ(1-11) displayed the same concentration-response curves in decreasing cAMP formation in HEK293 cells expressing NOP receptors only and in those coexpressing NOP and MOP receptors. Interestingly, Ro 64-6198 (Lee et al, 2011) and (+)-5a Compound (the current study), which activated a subset of NOP receptors in vlPAG neurons (Chiou et al, 2004;Liao et al, 2011b), also displayed similar potencies and efficacies in both cell lines. In HEK293 cells co-expressing NOP and MOP receptors, we have demonstrated dense colocalization of these two receptors on cell membrane (Lee et al, 2011).…”

“…Interestingly, Ro 64-6198 (Lee et al, 2011) and (+)-5a Compound (the current study), which activated a subset of NOP receptors in vlPAG neurons (Chiou et al, 2004;Liao et al, 2011b), also displayed similar potencies and efficacies in both cell lines. In HEK293 cells co-expressing NOP and MOP receptors, we have demonstrated dense colocalization of these two receptors on cell membrane (Lee et al, 2011). The high colocalization rate suggests the formation of heteromerized NOP-MOP receptors.…”

“…It can neither distinguish the subset of NOP receptors sensitive or insensitive to (+)-5a Compound/Ro 64-6198 (Chiou et al, 2004;Liao et al, 2011b) nor differentiate homomeric NOP receptors and NOP-MOP heteromeric receptors, which are very likely formed in cells co-expressing NOP and MOP receptors (Lee et al, 2011). Recently, N/OFQ was found to have the same affinity at the binding site of 125 I-[Tyr 10 ]N/ OFQ(1-11) in the brains of NOP receptor knock-out mice, as compared with the wild types (Majumdar et al, 2009).…”

“…The homogeneous time-resolved fluorescence (HTRF) cAMP assay was performed in HEK293 cells stably transfected with human NOP and MOP receptors, alone or in combination, as described previously (Lee et al, 2011). Briefly, HEK293 cells were dispensed with compound buffer in 96 half-well plates (Costar, Corning, NY, USA) on the day of the experiment.…”

“…[Tyr 10 ]N/OFQ(1-11), (+)-5a Compound, Ro 64-6198, SB-612111 and isobutylmethylxanthine were dissolved in dimethylsulfoxide (DMSO) and other drugs were dissolved in de-ionized water. The final concentration of DMSO was kept below 0.1%, which did not affect the membrane currents elicited by voltage ramps (Chiou et al, 2004) or cAMP assays (Lee et al, 2011).…”