RESUMO
Objective To investigate the endocytosis and exocytosis of soluble uranium in human kidney proximal tubular epithelial (HK-2) cells and the cytotoxicity after uranium exposure. Methods Cell Counting Kit-8 assay was used to determine the cell viability after different concentrations of uranium exposure, and optical microscopy and transmission electron microscopy were used to observe the changes in cells after uranium exposure. Inductively coupled plasma mass spectrometry was used to monitor the endocytosis and exocytosis of uranium over time by cells. Flow cytometry was used to assess the changes in cell cycle and apoptosis after uranium exposure. Results After uranium exposure, HK-2 cells showed dose-dependent damage; cell cycle was arrested in G1 phase; cell apoptosis and necrosis occurred; cell proliferation was inhibited. The content of endocytic uranium increased gradually within 24 h, and there was a threshold for uranium endocytosis, while the fraction of uranium binding to cell surface was low (< 0.2%). Over 40% of the endocytic uranium would be exocytosed within 1 h. Uranium could form needle-like precipitates in both intracellular and extracellular areas after uranium exposure. Conclusion After uranium exposure, cells show decreased viability, cell cycle arrest, and cell apoptosis. The process of endocytosis and exocytosis of soluble uranium is very rapid. HK-2 cells can convert soluble uranium into non-toxic precipitates.