title: Effects of nifedipine and Bay K 8644 on contractile activities in single skeletal muscle fibers of the frog.
abstract: The effects of dihydropyridine derivatives on contractile activity were examined in single fibers of frog skeletal muscles. Both nifedipine and Bay K 8644 enhanced twitch responses regardless of the presence or absence of Ca2+ without any effects on the resting membrane potential, evoked action potential and Ca2+ sensitivity of the contractile machinery. Twitch responses enhanced by Bay K 8644, but not by nifedipine, were partially reduced by adenine, an inhibitor of Ca(2+)-induced Ca2+ release from sarcoplasmic reticulum, suggesting the involvement of Ca(2+)-induced Ca2+ release in Bay K 8644-induced potentiation of the twitches. Both nifedipine and Bay K 8644 caused a dose-dependent potentiation of K+ contractures without any effects on the membrane potential in the presence of Ca2+, but inhibited the contractures in the absence of Ca2+. These results suggest that dihydropyridine derivatives modify contractile activities of skeletal muscles by modulating the dihydropyridine receptors on the surface of T-tubules acting as voltage sensors.
authors.affiliation: Department of Pharmacology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Kitamura
authors.forename: T
authors.initials: T
authors.lastname: Ohta
authors.forename: S
authors.initials: S
authors.lastname: Ito
authors.forename: Y
authors.initials: Y
authors.lastname: Nakazato
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects; D000225:Adenine / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects; D004095:Dihydropyridines / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D066298:In Vitro Techniques; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000166:cytology / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D004095:Dihydropyridines; D002110:Caffeine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D000225:Adenine; D011188:Potassium; D002118:Calcium