Ni3S2 uptake by lung cells and its interaction with plasma membranes

The uptake and biological transformation of Ni3S2 was studied on guinea pig alveolar macrophages (GPAM) in primary culture. Two different pathways are observed: (i) phagocytosis of alpha Ni3S2 crystals and subsequent degradation to minute particles, which are recovered bound to the membranes of phagocytic vacuoles and to lysosomal membranes. These degradation products contain sulphur in very reduced quantities, as revealed by energy-dispersive spectrometry (EDS). (ii) Extracellular degradation to regular round particles (0.1-0.2 microns) and irregular minute particles (10-30 nm). Round particles may enter the cell by pinocytosis and are characterized by the loss of sulphur. Minute particles are bound preferentially to cell membranes, to cytoplasmic organelles, such as endoplasmic reticulum, mitochondria and peroxysomes, to liposomes and to the euchromatinic part of nuclei. EDS analyses in these particles revealed the substitution of sulphur by phosphorus. This observation suggests the formation of an Ni-P complex with the phosphate groups of membranous and liposomal phospholipids and of the euchromatinic part of DNA or RNA. Steady-state fluorescence polarization analysis were carried out on GPAM and, for comparative purposes, on human embryonic pulmonary epithelial cells (L132 cell line). In both cell types they revealed a significant increase of membrane fluidity, induced either by desaturation of aliphatic chains or directly by the cleavage of fatty acid chains.