An analysis of post-contracture potentiation in frog twitch skeletal muscle.
Post-tetanic potentiation (PTP) was mimicked by post-contracture potentiation (PCP) in the twitch muscle of frog. A marked PCP was observed in small bundles of semitendinosus muscle in tetrodotoxin (TTX)-containing solution under current clamp condition. Contractures were induced by a constant depolarizing current pulse of 1 s every 5 min. Each contracture (C) was preceded and followed by a twitch-corresponding short contracture, T1 and T2, with an interval of 2 s. The ratio of twitch height, T2/T1, was measured and compared under various conditions. In TTX-containing Ringer solution, T2/T1 depended on magnitude of both T and C. When T2/T1 was plotted against C/T1 a quasi-linear relationship was found. The slope of the curve was 0.076 and was found to decrease when the duration of T was increased to 1 s. In TTX-containing solution, addition of 2 mM Ba2+ or 1 mM caffeine potentiated T as well as C but decreased T2/T1 markedly. Similar effects were observed when Na+ was replaced with TEA+ or when bath temperature was lowered from 20 to 8 degrees C. In all cases T2/T1 vs. C/T1 curve was shifted to the left and downwards. It was considered that these results could be attributable to an elevation of the resting Ca2+ concentration in the sarcoplasm. Thus the phenomenon of PCP probably reflects the time course of Ca2+ transients in the conditioning contracture C.
Kawata
H
H
Department of Physiology, School of Medicine, Fukuoka University, Japan.
Hatae
J
J
D000200:Action Potentials; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D011898:Ranidae; D013696:Temperature; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin
D013757:Tetraethylammonium Compounds; D001464:Barium; D002110:Caffeine; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D002118:Calcium