EFFECTS OF INORGANIC MERCURY AND METHYLMERCURY ON THE IONIC CURRENTS OF CULTURED RAT HIPPOCAMPAL-NEURONS

1. The effects of inorganic Hg2+ and methylmercuric chloride on the io nic currents of cultured hippocampal neurons were studied and compared . We examined the effects of acute exposure to the two forms of mercur y on the properties of volt age - activated Ca2+ and Na+ currents and N-methyl-D-aspartate (NMDA)-induced currents. 2. High-voltage activate d Ca2+ currents (L type) were inhibited by both compounds at low micro molar concentrations in an irreversible manner. Mercuric chloride was five times as potent as methylmercury in blocking L-channels. 3. Both compounds caused a transient increase in the low-voltage activated (T- type) currents at low concentrations (1 mu M) but blocked at higher co ncentrations and with longer periods of time. 4. Inorganic mercury blo ckade was partially use dependent, but that by methylmercury was not. There was no effect of exposure of either form of mercury on the I-V c haracteristics of Ca2+ currents. 5. Na+- and NMDA-induced currents wer e essentially unaffected by either mercury compound, showing only a de layed nonspecific effect at a time of overall damage of the membrane. 6. We conclude that both mercury compounds show a relatively selective blockade of Ca2+ currents, but inorganic mercury is more potent than methylmercury.