FLUORIDE-ION TOXICITY IN HUMAN KIDNEY COLLECTING DUCT CELLS

Background: Several halogenated anesthetics induce a urinary concentra ting defect, partly related to fluoride ion toxicity in collecting duc t cells. The aim of this study was to investigate the effects of fluor ide ion in human kidney cells. Methods: Immortalized human collecting duct cells were used. In a first set of experiments, the toxicity thre shold concentration was determined by exposing cell cultures for 24 h to increasing concentrations of fluoride ion in the medium: 0, 1, 5, a nd 10 mM. The second set of experiments was a time-effect study in whi ch cells were exposed to 5 mM fluoride for 2, 6, and 24 h. Assessment of toxicity was based on several endpoints: cell number, protein conte nt, H-3-leucine incorporation in newly synthesized proteins, extracell ularly released lactate dehydrogenase, Na-K-ATPase pump activity, and electron microscope studies. Results: After 24 h of exposure, fluoride ion decreased cell number (-23%, P < 0.05), total protein content (-3 0%, P < 0.05), and 3H-leucine incorporation (-43%, P < 0.05) and in cr eased lactate dehydrogenase release (+236%, P < 0.05) at a threshold c oncentration of 5 mM. Fluoride ion also inhibited Na-K-ATPase activity at 5 mM (-58%, P < 0.05). Major morphologic alterations of mitochondr ia, including crystal formation, were detected from 1 mM fluoride conc entration. Time-effect studies showed that, after only 6 h of exposure at 5 mM, fluoride decreased cell number (-13%, P < 0.05), H-3-leucine incorporation (-48%, P < 0.05), and Na-K-ATPase activity (-20%, P < 0 .05) and increased lactate dehydrogenase release (+145%, p < 0.05). Cr ystal deposits in mitochondria again were a more sensitive marker of c ell injury, detectable after only 2 h of exposure. Conclusions: These results suggest that the mitochondrion is a target of fluoride toxicit y in human collecting duct cells, and its alteration is partly respons ible for the sodium and water disturbances observed in patients.