Methylmercury modulates GABAA receptor complex differentially in rat cortical and cerebellar membranes in vitro.

Effects of methylmercury (MetHg) on the specific [3H]flunitrazepam binding were studied in rat cortical and cerebellar P2-fractions in vitro. MetHg did not affect significantly the specific [3H]flunitrazepam binding in unwashed P2-fraction but increased it marginally (by 16%) at 100 microM in washed P2-fraction, in both brain regions. Muscimol (3 microM), a GABAA agonist, stimulated the [3H]flunitrazepam binding by 30% to 50% depending on the brain region. In washed cerebellar membranes the enhancing response of muscimol was 10 to 14% lower after preincubation of the tissue with MetHg but in cerebral cortex MetHg did not modulate the muscimol response at all. The results indicate that Met-Hg may have region specific effects on GABAA receptors in vitro and the effect may depend on the occupational state of the GABA binding domain of the receptor complex.