A comparison of the effects of aminopyridines on isolated chicken and rat skeletal muscle preparations

1. 1. In the chick biventer cervicis preparation, 4-aminopyridine and 3,4-diaminopyridine selectively augmented indirectly elicited twitches. 2. 2. In the rat hemidiaphragm preparation, both indirectly and directed elicited twitches were augmented. The augmentation was more rapid for indirectly elicited twitches and the twitches became repetitive. 3. 3. The aminopyridines are concluded to facilitate neuromuscular transmission in both species, but increase contractility only in rat. 4. 4. The aminopyridines are suggested to act mainly by inhibiting membrane potassium conductance. Aminopyridine binding sites on the potassium channels may be different in chick and rat muscle. Alternatively, augmentation of contractility in the rat may involve an additional mechanism.