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  • Title: Opioid-induced increase in [Ca2+]i in ND8-47 neuroblastoma x dorsal root ganglion hybrid cells is mediated through G protein-coupled delta-opioid receptors and desensitized by chronic exposure to opioid.
    Author: Tang T, Kiang JG, Cote T, Cox BM.
    Journal: J Neurochem; 1995 Oct; 65(4):1612-21. PubMed ID: 7561856.
    Abstract:
    delta-Receptor agonists induce a concentration-dependent increase in intracellular calcium concentration ([Ca2+]i) in ND8-47 cells by activating dihydropyridine-sensitive Ca2+ channels. The role of G proteins in transducing the opioid effect has been studied. Pretreatment of cells with pertussis toxin (100 ng/ml, 24 h) almost completely blocked [D-Ser2,Leu5]enkephalin-Thr (DSLET)-induced increase in [Ca2+]i. Cholera toxin (10 nM, 24 h) had no effect on DSLET-induced response. Pretreatment of the cells with 1 microM DSLET for 1 h resulted in a 30% inhibition of DSLET-induced increase in [Ca2+]i and a 78% inhibition after exposure for 24 h. After 1 h of exposure to DSLET, there was a decrease in agonist affinity with no significant changes in receptor density. Cells exposed to 1 microM DSLET for 24 h demonstrate a nearly 90% decrease in [3H]diprenorphine binding, with a decrease in affinity for agonist at the remaining binding sites. G protein subunits alpha i2, alpha i3, alpha s, and alpha q were detected in ND8-47 cell membranes by western blot; alpha o and alpha i1 were not present. Chronic DSLET treatment had no significant effect on the quantity of each of the alpha-subunits. These results suggest that the DSLET-induced increase in [Ca2+]i mediated through pertussis toxin-sensitive G proteins (probably Gi2 or Gi3) and the attenuation of this response in chronically treated cells is associated with a relatively rapid reduction in receptor affinity to DSLET and a slow reduction in receptor density.
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