Hg2+ and small-sized polyethylene glycols have inverse effects on membrane permeability, while both impair neutrophil cell motility.

Toxic effects after exposure to mercury are well documented in human. Little is, however, known about how Hg 2 + affect host defense in general and neutrophil functions in particular. We show here that exposure of human neutrophils to HgCl 2 dose-dependently impairs chemoattractant-stimulated motility. Long-term exposure (5-10 min) to Hg 2 + yields a rapid influx of extracellular Ca 2 + followed by leakage of cytosolic fluorophores, as assessed using fura-2 and ratio imaging microscopy. The inhibition on motility was partly reversible, since pre-treated neutrophils placed in an Hg 2 + -free environment displayed higher migration rates. The Hg 2 + -induced fluxes were prevented by addition of small-sized polyethylene glycols (PEG 200-400), which also dose-dependently inhibited neutrophil transmigration. Localized, minute micropipette additions of Hg 2 + or PEG caused retraction of the leading edge and redirection of cell migration. Since Hg 2 + increases and PEGs decrease membrane permeability in a partially competitive manner, we suggest that the known aquaporin-inhibitor Hg 2 + alters membrane permeability by affecting the bidirectional flux through the leukocyte aquaporin-9 (AQP9) while small-sized PEGs yield decreased membrane permeability by becoming trapped in the promiscuous channel. The local additions of Hg 2 + or PEG probably force other cell regions to take over from those with blocked AQPs. Hence, the cells turn direction of motility away from the micromanipulator needle.