Benzoquinonium dibromide

Benzoquinonium Dibromide (BZQ) is an inhibitor of acetylcholine receptor (AChR) and ganglion. BZQ activates nicotinic single channels but blocks open channels at the neuronal AChRs.
AChR is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter. Nicotinic acetylcholine receptor (nAChR) are particularly responsive to nicotine and is a Na+ and K+ channel.
The effects of BZQ on α-BGT sensitive neuronal nAChRs were evaluated on outside-out patches excised from fetal rat hippocampal neurons cultured for 11 to 35 days and found that BZQ (0.1-10 μM) could activate single-channel currents. BZQ was also able to activate various channel conductance states. The two most frequently encountered conductance states activated by BZQ were 43 ± 3.3 pS and 30 ± 4.2 p5. In frog muscle fibers, BZQ is an open-channel blocker of the nAChR and also activates single-channel currents that are not blocked by a-BGT.
References:
[1]. Pereira EF, Reinhardt-Maelicke S, Schrattenholz A, et al. Identification and functional characterization of a new agonist site on nicotinic acetylcholine receptors of cultured hippocampal neurons. J Pharmacol Exp Ther, 1993, 265(3): 1474-1491.

Identification and functional characterization of a new agonist site on nicotinic acetylcholine receptors of cultured hippocampal neurons.[Pubmed:8510023]

J Pharmacol Exp Ther. 1993 Jun;265(3):1474-91.

Electrophysiological and biochemical techniques were used to demonstrate that alpha-bungarotoxin-, methyllycaconitine-sensitive neuronal nicotinic acetylcholine receptors (nAChRs) can be activated via a novel agonist site(s). The residue proposed to be essential to this site is the amino acid Lys-125 of the receptor alpha subunit. In outside-out patches excised from cultured hippocampal neurons, physostigmine (PHY) and 1-methyl-PHY activated single channels whose main conductances were 46 and 23 pS. This action was insensitive to DL-2-amino-5-phosphonovaleric acid, atropine, tetrodotoxin and competitive nicotinic antagonists, but blocked by benzoquinonium or FK1, a nAChR-specific antibody raised against rat muscle nAChR alpha subunits that binds to the novel site. Indirect immunofluorescence staining demonstrated that FK1 binds to the hippocampal neurons, as would be expected based on the high degree of homology among nAChR alpha subunits from diverse sources in the region surrounding Lys-125. PHY prevented the binding of FK1, thus supporting that FK1 is a specific probe for the PHY site. High-affinity sites (KD approximately 35 nM) for 1-methyl-PHY were identified in hippocampal neurons. Similar to PHY, benzoquinonium (0.1-10 microM) and galanthamine (1-10 microM) activated nicotinic single channels. The agonists benzoquinonium and PHY were also open-channel blockers at the neuronal nAChRs, whereas galanthamine was predominantly a desensitizing agent. In mouse fibroblasts transfected with cDNAs of alpha 4 and beta 2 neuronal nAChR subunits, PHY also activated single channels that were blocked by FK1. In these cells, dihydro-beta-erythroidine blocked single channels activated by (+)-anatoxin-a and did not affect those opened by PHY. Thus, the present results suggest that the novel agonist site located on the receptor alpha subunit is a common feature of neuronal nAChRs.