Extracellular requirements for the endocytosis of carcinogenic crystalline nickel sulfide particles by facultative phagocytes.

Various culture medium components were examined for their effect upon the phagocytosis of carcinogenic crystalline and non-carcinogenic amorphous NiS by cultured fibroblastic cells using both a visual and radioactive assay for phagocytosis. Crystalline NiS was phagocytosed by cells in a simple salts/glucose maintenance medium to an extent similar to that observed in complex culture medium fortified with 10% fetal bovine serum (FBS), suggesting that serum proteins and other components in complex culture medium exert little influence upon the uptake of these heavy metal particles. Phagocytosis of crystalline NiS was shown to be highly dependent upon Ca2+ since omission of Ca2+ from the salts/glucose medium substantially reduced phagocytosis, while readdition of Ca2+ stimulated uptake in a concentration-dependent manner. The uptake of the NiS particles was inhibited by trifluoperazine, a calmodulin antagonist, implicating intracellular Ca2+ in this phagocytosis process. Since the opposite surface charge of crystalline and amorphous NiS has been related to their different phagocytic uptake by cells whose primary function is not phagocytosis (facultative phagocytes), these results show that the culture medium components do not modify the surface charge of these particles in a way that significantly influences their uptake.