A local anesthetic, tetracaine, similarly inhibits Ag+ and K+ contractures in frog skeletal muscle.
To evaluate usefulness of Ag+ contracture as a tool for elucidating the mechanism underlying the excitation-contraction coupling, the effects of tetracaine on Ag+ contracture were compared with those on K+ and caffeine contractures in frog skeletal muscle. Tetracaine less than 100 microM shortened the duration of 120 mM K+ contracture, without affecting tension amplitude. At higher concentrations of tetracaine, K+ contracture was inhibited dose-dependently and the duration shortened. Treatment of the fibers with 20-500 microM tetracaine for 3 min did not block the contracture induced by 25 mM caffeine. Effects of tetracaine on Ag+ contracture were similar to those on K+ contracture. In the presence of 200 microM tetracaine, 41% inhibition was observed in 120 mM K+ contracture, while 43% in 100 microM Ag+ contracture. Also, 200 microM tetracaine completely inhibited the contractures induced by 40 mM K+ or 5 microM Ag+. These findings suggest that the Ag+ may induce contractures via its action on the T/SR junction, not a direct action on the SR. Therefore, understanding the mechanism involved in the development of Ag+ contracture would be helpful to elucidate the mechanism of excitation-contraction coupling.
D000200:Action Potentials / Q000187:drug effects; D000779:Anesthetics, Local; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000502:physiology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011892:Rana catesbeiana; D012834:Silver / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013748:Tetracaine / Q000494:pharmacology*
D000779:Anesthetics, Local; D013748:Tetracaine; D002110:Caffeine; D012834:Silver; D011188:Potassium