In vitro effect of organic and inorganic mercury on the serotonergic system

Interactions of organic (methyl mercury) and mineral (acetate, chloride, nitrate: Hg2+) mercury salts with the serotonergic systems were studied in vitro using synaptosomal fractions prepared from rat brain cortex preloaded with [3H]5-HT. In the absence of calcium, mercury salts induced a spontaneous release of the amine corresponding to a total depletion of the synaptosomal content. EC50 for the organic and mineral forms of the ion were 66 +/- 2 microM and 107 +/- 16 microM respectively. In the presence of calcium (2.4 mM) a similar pattern of release was observed except that an additional release was induced by mineral mercury at low concentration (EC50 = 8.4 +/- 1.3 microM) which corresponded to a maximal release of 18.6 +/- 3.5% of the synaptosomal content. Therefore, the latter release appears calcium-dependent. Parallelly, the effects of mercury salts have been examined on the binding of [3H]5-HT to its high affinity 5-HT1 sites; organic and mineral mercury inhibited the binding with IC50 of 27.8 +/- 3.2 microM respectively. These results show that mercury ions interact with the serotonergic system by different mechanisms depending on their concentrations and their ionic forms.