The actions of three diaminopyridines on the chick biventer cervicis muscle.

The effects of 2,3-, 2,6- and 3,4-diaminopyridine were investigated on the isolated chick biventer cervicis muscle preparation. All three compounds reversed tubocurarine blockade and augmented twitch height in indirectly stimulated preparations. Less twitch augmentation was observed in directly stimulated preparations. 3,4-Diaminopyridine was the most effective of the compounds in facilitating neuromuscular transmission, but exhibited less convulsant activity than 4-aminopyridine. 3,4- and 2,3-diaminopyridine in high concentrations caused contractures that were inhibited by erabutoxin b or by beta-bungarotoxin. It is suggested that the diaminopyridines increase both evoked and spontaneous acetylcholine release.