Multiple effects of mercury on cell volume regulation, plasma membrane permeability, and thiol content in the human intestinal cell line Caco-2

In a previous study, we characterized Cd-Hg interactions for uptake in human intestinal Caco-2 cells. We pursued our investigations on metal uptake from metal mixtures, focusing on the effects of Hg on cellular homeostasis. A 4-fold higher equilibrium accumulation value of 0.3 mu mol/L Hg-203 was measured in the presence of 100 mu mol/L unlabeled Hg in the serum-free exposure medium without modification in the initial uptake rate. This phenomenon was eliminated at 4 degrees C. Mercury induced an increase in tritiated water and [H-3] mannitol uptakes for exposure times greater than 20 min. Incubations for 20 min and 30 min with 100 mu mol/L Hg and 2 mmol/L N-ethylmaleimide (NEM) resulted in a 34% and 50% reductions in cellular thiol staining, respectively, with additive effects. Lactate dehydrogenase leakage and live/dead assays confirmed the maintenance of cell membrane integrity in Hg- or NEM-treated cells. We conclude that Hg may alter membrane permeability and increase cell volume without any loss in cell viability. This phenomenon is sensitive to temperature and could involve Hg interaction with membrane thiols, possibly related to solute transport. During metal uptake from metal mixtures, Hg may thus promote the uptake of other toxic metals by increasing cell volume and consequently cell capacity.