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Mg2 decreased basal and GABA-inhibited t-butylbicyclophosphoro[35S]thionate binding to GABAA receptor ion channels in rat brain sections up to 1 mM, but increased the binding at 10 mM. The Mg2 -effect was detectable in the presence of a specific GABA site competitive antagonist. Two-electrode voltage clamp recordings of recombinant [alpha]1[beta]2[gamma]2S, [alpha]1[beta]2, [alpha]2[beta]2[gamma]2S and [alpha]2[beta]2 GABAA receptors revealed a potentiation by 0.1-1 mM Mg2 of EC20 GABA-evoked ion currents. At 10 mM, Mg2 decreased the currents. In the absence of GABA, Mg2 did not evoke any currents. The results show that physiologically relevant Mg2 concentrations affect the GABA responses on GABAA receptors in native and the main recombinant receptor subtypes, suggesting putative Mg2 binding sites on the receptor complex.

(C) 2001 Lippincott Williams & Wilkins, Inc.