cis-3,3'-Bis-[α-(trimethylammonium)methyl]azobenzene (cis-Bis-Q). Purification and properties at acetylcholine receptors of electrophorus electroplaques

The cis and trans isomers of the photoisomerizable compound, 3,3'-bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q), were purified by high-performance liquid chromatography using the ion-pair partitioning techique on a reverse-phase column. Solutions of cis-Bis-Q are stable at -20°C; at 25°C, thermal isomerization proceeds at a rate of 0.65%/day, cis-Bis-Q is less than 1% as potent a nicotinic agonist as the trans configuration. At concentrations of 1.5 μM or less, cis-Bis-Q exerts little or no blockade of the conductances induced by agonists. In voltage-clamped Electrophorus electroplaques exposed to cis-Bis-Q, laser flashes induce cis→trans photoisomerizations and increase the agonist-induced current by a factor of 20 within a few milliseconds.