Opiate-dependent modulation of adenylate cyclase.

Abstract

Reactions mediated by the opiate receptors that inhibit adenylate cyclase (EC 4.6 (1-3). However, exposure of cells to an opiate for 12 or more hours results in a compensatory increase in adenylate cyclase activity that is long-lived and not readily reversed by withdrawal of the opiate (4-6). Similar dual regulations of adenylate cyclase activity are mediated by a-adrenergic receptors (7) and excitatory muscarinic acetylcholine receptors (S. K. Sharma and M. Nirenberg, unpublished data; ref. 8). Thus, dual regulation may be a general regulatory mechanism which alters the responsiveness of adenylate cyclase to activations mediated by other species of receptors. Because the mechanism of coupling inhibition of adenylate cyclase with a subsequent increase in enzyme activity is unknown, we examined the properties of adenylate cyclase from control cells and cells treated with opiates. MATERIALS AND METHODSThe source of each chemical, growth conditions for culturing neuroblastoma X glioma NG108-15 hybrid cells, and preparation of homogenates have been described (2). Adenylate cyclase activity was measured by the procedure of Salomon et al. RESULTSEffect of Activators of Adenylate Cyclase. If the increase in adenylate cyclase activity of opiate-treated NG108-15 cells were due primarily to an increase in the number of molecules of adenylate cyclase, the relatively high enzyme activity of opiate-treated cells should be maintained under other assay conditions. For this reason, we studied the effects of activators and inhibitors on adenylate cyclase of cells growmn in the presence or absence of morphine or etorphine for S35 days. Sodium fluoride is known to activate basal adenylate cyclase and inhibit activation of the enzyme by hormones, presumably by uncoupling the enzyme from the hormone-receptor complex (10).The effects of NaF upon basal and prostaglandin El (PGE1)-stimulated adenylate cyclase activity from control or etorphine-treated NG108-15 cells as a function of time are shown in Fig. 1. In the presence of 8 mM NaF, the basal activities of adenylate cyclase from control and opiate-treated cells were increased 4.3-and 2.6-fold, respectively, and the specific activities of the two enzyme preparations then were similar.Conversely, the activities of PGEI-stimulated adenylate cyclase from control and opiate-treated cells were inhibited 44% and 60%, respectively, by NaF and the final specific activities were similar. These results show that adenylate cyclase from control cells is more responsive to activation by NaF than adenylate cyclase of opiate-treated cells and raise the possibility that the relatively high activity of adenylate cyclase of opiate-treated cells may be due to enzyme activation rather than to an increase in the number of enzyme molecules.

κ‐Opioid receptor‐transfected cell lines: modulation of adenylyl cyclase activity following acute and chronic opioid treatments

“…The reduction in cAMP levels during the agonist opiate exposure could initiate a cascade of cellular changes, which could lead to up-regulation of the amount and/or activity of AC [7,20]. Enhanced coupling of the stimulatory PGEj receptor to Gs or elevated levels of functionally intact Gs proteins were proposed by Ammer and Schulz [4,5] for opioid-treated NG108-15 and SH-SY5Y cells.…”

“…Chronic activation of opioid receptors in NG108-15 neuroblastoma x glioma cell line (containing g-receptors), as well as in the human neuroblastoma SH-SY5Y (containing mainly preceptors and some g-receptors), followed by the withdrawal of the opioid agonist, was shown to lead to AC supersensitivity ('overshoot') [4][5][6][7][8]. It has been suggested that this phenomenon represents a possible cellular adaptation mechanism associated with chronic opioid exposure.…”

Nucleus accumbens AGS3 expression drives ethanol seeking through Gβγ

“…Since the first characterization of cellular responses to EtOH (10) and other commonly abused drugs (11), molecules involved in G protein signaling have received much attention in the addiction literature (cf. refs.…”

Human μ-opioid receptor overexpressed in Sf9 insect cells functionally coupled to endogenous Gi/o proteins

“…In mammalian cells, opioid receptors couple to inhibitory G proteins of the G i/o family and inhibit the adenylyl cyclase [22]. Agonists DAGO and Ohm inhibited 10 μ M forskolin-stimulated increase in intracellular cAMP production in a dose-dependent manner with IC 50 values of 0.9 nM and 0.3 nM, respectively (Fig 4A).…”