Rates and equilibria for a photoisomerizable antagonist at the acetylcholine receptor of Electrophorus electroplaques.

Voltage-jump and light-flash experiments have been performed on isolated Electrophorus electroplaques exposed simultaneously to nicotinic agonists and to the photoisomerizable compound 2,2'-bis-[alpha-(trimethylammonium)methyl]-azobenzene (2BQ). Dose-response curves are shifted to the right in a nearly parallel fashion by 2BQ, which suggests competitive antagonism; dose-ratio analyses show apparent dissociation constants of 0.3 and 1 microM for the cis and trans isomers, respectively.