(-)-Bicuculline methiodide

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Background

(-)-Bicuculline methiodide is an antagonist of γ-aminobutyric acid-A (GABAA) receptor, with IC50 value of 500 μM for GABA binding [1].
Three classes of GABA receptors have been characterized based on their pharmacology, namely GABAA, GABAB and GABAC receptors, among which GABAA and GABAC receptors are ligand-gated chloride (Cl-) channels. GABA receptors play important roles in central nervous system by responding to the inhibitory neurotransmitter GABA [2].
On synaptic membranes of chick cerebellum at birth, (-)-bicuculline methiodide acted as a less potent convulsant than (+)-Bicuculline methiodide which was more effective in displacing GABA binding, with an IC50 value of 10 μM [1]. In C. elegans, (-)-bicuculline methiodide at the concentration of 10 μM did not inhibit UNC-49B homomeric or UNC-49B/C heteromeric receptors which are UNC-49 subunits most closely related to the bicuculline- and benzodiazepine-insensitive RDL GABA receptors of insects. (-)-Bicuculline methiodide was used to confirm that the UNC-49 receptors were pharmacologically distinct from the mammalian GABAA receptors [3].

[1]. Fiszer De Plazas S. Ontogenesis of GABA receptor sites in chick embryo cerebellum. Brain Research, 1982, 255(2): 263-275.
[2]. Goutman J D, Calvo D J. Studies on the mechanisms of action of picrotoxin, quercetin and pregnanolone at the GABA rho 1 receptor. British Journal of Pharmacology, 2004, 141(4): 717-727.
[3]. Bamber B A, Twyman R E, Jorgensen E M. Pharmacological characterization of the homomeric and heteromeric UNC-49 GABA receptors in C. elegans. British Journal of Pharmacology, 2003, 138(5): 883-893.