title: Post-tetanic potentiation and inhibition in single fibres isolated from frog semitendinosus muscle.
abstract: The twitch contractions of single fibres from the frog semitendinosus, innervated and denervated, were studied after a brief period (2-3 sec) of conditioning stimulation (CS), at frequencies varying from 1-120/sec. Twitch potentiation was consistently observed in denervated fibres at all rates of CS used. Maximal potentiation was attained within the first 12 sec after the end of CS, which then decayed progressively. The overall duration of the effect, in general, was longer than 5 min. The time course of potentiated twitches was slightly shortened. Inhibition preceding potentiation was the prevailing effect on innervated fibres under the present conditions. Inhibition appeared either after a short interval (500 msec of less) between the end of CS and the beginning of the subsequent twitch, or after several repetitions of the conditioning schedule. The latter form of inhibition was replaced by potentiation when the corresponding fibres were allowed to rest for 60 min before further conditioning stimulations. Maximal inhibition was attained shortly after the end of CS, which then progressively disappeared. On occasion inhibition lasted longer than 5 min. The time course of inhibited twitches was slightly enlarged. After fatigue, CS produced twitch inhibition on innervated fibres. In denervated muscles the effect was either potentiation or inhibition. These results are discussed according to the data in the literature.
mesh_terms: D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009121:Muscle Denervation; D009132:Muscles / Q000378:metabolism; D009433:Neural Inhibition; D011894:Rana pipiens
chemical_list: D002118:Calcium