DUAL SIGNAL-TRANSDUCTION THROUGH DELTA-OPIOID RECEPTORS IN A TRANSFECTED HUMAN T-CELL LINE

Opiates are known to function as immunomodulators, in part by effects on T cells. However, the signal transduction pathways mediating the ef fects of opiates on T cells are largely undefined, To determine whethe r pathways that regulate free intracellular calcium ([Ca2+](i)) and/or cAMP are affected by opiates acting through delta-type opioid recepto rs (DORs), a cDNA encoding the neuronal DOR was expressed in a stably transfected Jurkat T-cell line, The DOR agonists, deltorphin and [D-Al a(2),D-Leu(5)]-enkephalin (DADLE), elevated [Ca2+](i), measured by flo w cytofluorometry using the calcium-sensitive dye, Fluo-3, At concentr ations front 10(-11)-10(-7) M, both agonists increased [Ca2+](i) from 60 nM to peak concentrations of 400 nM in a dose-dependent manner with in 30 sec (ED(50) of approximate to 5 x 10(-9) M). Naltrindole, a sele ctive DOR antagonist, abolished the increase in [Ca2+](i), and pretrea tment with pertussis toxin was also effective. To assess the role of e xtracellular calcium, cells were pretreated with EGTA, which reduced t he initial deltorphin-induced elevation of [Ca2+](i) by more than 50% and eliminated the second phase of calcium mobilization. Additionally the effect of DADLE on forskolin-stimulated cAMP production was determ ined, DADLE reduced cAMP production by 70% (IC50 of approximate to 10( -11) M), and pertussis toxin inhibited the action of DADLE. Thus, the DOR expressed by a transfected Jurkat T-cell line is positively couple d to pathways leading to calcium mobilization and negatively coupled t o adenylate cyclase. These studies identify two pertussis toxin-sensit ive, G protein-mediated signaling pathways through which DOR agonists regulate the levels of intracellular messengers that modulate T-cell a ctivation.