Morphine coupling to invertebrate immunocyte nitric oxide release is dependent on intracellular calcium transients

Morphine significantly stimulated invertebrate immunocyte intracellular calcium level increases in a concentration-dependent manner in cells preloaded with Fura 2/AM. Morphine's action was blocked by prior exposure of the cells to the opiate receptor antagonist naloxone. Various opioid peptides did not exhibit this ability, indicating a morphine-mu 3 mediated process. In comparing the sequence of events concerning morphine's action in stimulating both [Ca2+]i and NO production in these cells, we found that the first event precedes the second by 42 +/- 7 s. The opiate stimulation of [Ca2+]i- was attenuated in cells leached of calcium. strongly suggesting that intracellular calcium levels regulate cNOS activity in invertebrate immunocytes.