Different stimulatory opioid effects on intracellular Ca in SH-SY5Y cells

Present study revealed the stimulatory effects of δ opioid receptor on intracellular Ca²⁺ concentration (Ca²⁺]_i) in SH-SY5Y cells. Fura-2 based single cell fluorescence ratio (F345/F380) was used to monitor the fluctuation of Ca²⁺]_i. Application of the selective delta-opioid receptor agonist alone, D-Pen^2,5]-enkephalin (DPDPE), hardly had any effects on cells cultivated for 3–10 days. However, after the cells had been pre-stimulated with cholinoceptor agonist, carbachol, variable calcium elevation was found in 59% of the cultures. The response was naltridole-reversible and dose-dependent, and was abolished completely by thapsigargin (TG) treatment but not by administration of CdCl₂ or 0-Ca²⁺ bath solutions. DPDPE-mediated Ca²⁺]_i elevation was abolished by pertussis toxin (PTX) pretreatment but not cholera toxin (CTX), indicating coupling via G proteins of G_i/G_o subfamily. In 17.5% of the responding cells, biphase response was found which may be due to both the stimulatory and the inhibitory effects of opioid. On the other hand, in acutely dissociated cells, DPPDE alone induced Ca²⁺]_i increase in 50% of the cultures. The probability and the amplitude of the elevation were decreased considerably by application of nifedipine or 0-Ca²⁺ bath solution and was little affected by application of TG. DPDPE activated Ca²⁺]_i increase via a PTX-insensitive and CTX-sensitive pathway suggesting coupling through G_s subunit. All these indicated the opioid modulated the intracellular Ca²⁺ regulation system through different pathways. SH-SY5Y cell line might be a suitable model for the investigation of the complex mechanism which underlies opioid function.