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Opioid‐Induced Increase in [Ca 2+ ] i in ND8‐47 Neuroblastoma × Dorsal Root Ganglion Hybrid Cells Is Mediated Through G Protein‐Coupled δ‐Opioid Receptors and Desensitized by Chronic Exposure to Opioid
Author(s) -
Tang Tianlai,
Kiang Juliann G.,
Cote Thomas,
Cox Brian M.
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.65041612.x
Subject(s) - dorsal root ganglion , opioid , chemistry , chronic pain , μ opioid receptor , receptor , neuroblastoma , dorsum , biophysics , medicine , endocrinology , neuroscience , biochemistry , anatomy , biology , cell culture , genetics
δ‐Receptor agonists induce a concentration‐dependent increase in intracellular calcium concentration ([Ca 2+ ] i ) in ND8‐47 cells by activating dihydropyridine‐sensitive Ca 2+ 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 ‐Ser 2 ,Leu 5 ]enkephalin‐Thr (DSLET)‐induced increase in [Ca 2+ ] i . Cholera toxin (10 n M , 24 h) had no effect on DSLET‐induced response. Pretreatment of the cells with 1 µ M DSLET for 1 h resulted in a 30% inhibition of DSLET‐induced increase in [Ca 2+ ] 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 µ M DSLET for 24 h demonstrate a nearly 90% decrease in [ 3 H]diprenorphine binding, with a decrease in affinity for agonist at the remaining binding sites. G protein subunits α i2 , α i3 , α s , and α q were detected in ND8‐47 cell membranes by western blot; α o and α i1 were not present. Chronic DSLET treatment had no significant effect on the quantity of each of the α‐subunits. These results suggest that the DSLET‐induced increase in [Ca 2+ ] i is mediated through pertussis toxin‐sensitive G proteins (probably G i2 or G i3 ) 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.