The effect of δ-opioid agonists on intracellular calcium level in MOLT-4 T-cell line

δ-opioid agonists were reported to affect T cell functions: proliferation, cytotoxicity, cytokine production. Changes in intracellular calcium level are important in T-cell activation. In this study the effect of the synthetic δ-opioid agonist DADLE and an endogenous δ-opioid pentapeptide Met-enkephalin on the intracellular calcium level in human T-lymphoblastic leukemia MOLT-4 cells is reported. Intracellular calcium level was monitored using QUIN 2-AM as a fluorescent dye in MOLT-4 cells after short treatment (2 and 15 min) with DADLE and Met-enkephalin. DADLE (10^-8M) mildly (average 28%) decreased the intracellular calcium level after 1 min treatment. The suppressive effect of DADLE (10^-8M) on the intracellular calcium level was enhanced by longer (15 min) treatment of MOLT-4 cells (average 40%). Met-enkephalin (10^-9M - 10^-7M) decreased (average 33 %) the intracellular calcium level after 2 min treatment (average 33% - 37%). However, Met-enkephalin (10^-7M) increased (average 31%) the intracellular calcium level after longer (15 min) treatment. Ionophore A23187 (10^-7M, 10^-6M) was used as a positive control to enhance intracellular calcium level. Thus, δ-opioid agonist DADLE decreased basal intracellular calcium level in MOLT-4 cells after short treatment, while endogenous Met-enkephalin altered intracellular calcium level in a bidirectional way by decreasing and increasing it.