Uptake of HgCl2 and MeHgCl in an insect cell line (Aedes albopictus C6/36)

We studied the uptake mechanism of mercuric chloride (Hg) and methylmercuric chloride (MeHg) in Aedes albopictus C6/36 cells. The uptake kinetics, together with the effect of temperature and a metabolic inhibitor (2, 4-dinitrophenol) on the mercury accumulation, were examined. Both amounts of internalized Hg and MeHg increased linearly with the extracellular concentration. Initially, the influx rate was high for both metal species but MeHg was found to accumulate seven times faster than Hg. At longer exposure times it leveled off for Hg, while for MeHg, the intracellular concentration decreased. Hg toxicity was not significantly influenced by elevated temperatures; in contrast there was a marked decrease of the LC50/24h value for MeHg. On the other hand, Hg accumulation was temperature dependent but MeHg was not. The different toxicity and uptake rate of both mercury compounds can be explained in terms of membrane permeability and target site. For Hg the main target seems to be the plasma membrane, while MeHg readily crosses this barrier and reacts with intracellular targets. 2, 4-Dinitrophenol had no effect on the accumulation of Hg but that of MeHg was doubled. This increased MeHg accumulation might be the result of the inhibition of an active MeHg efflux mechanism; this is in agreement with the MeHg influx kinetics. Despite these differences between Hg and MeHg, which probably result from their physicochemical properties, our experiments indicate that, for both mercury species, simple diffusion is probably the main way to entrance in Aedes cells.