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

Morphine significantly stimulated invertebrate immunocyte intracellular cal cium level increases in a concentration-dependent manner in cells preloaded with Fura(TM) 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 stimul ating both [Ca2+](i) and NO production in these cells, we found that the fi rst 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 immunoc ytes. (C) 1999 Elsevier Science Inc. All rights reserved.