title: Nitrendipine blocks high potassium contractures but not twitches in rat skeletal muscle.
abstract: The effects of the organic calcium channel blocker nitrendipine was tested on electrically evoked twitches and on potassium depolarization-induced contractures of rat lumbricalis muscles. Nitrendipine (10(-7) to 5 X 10(-5) M) blocked only the potassium contractures. It was concluded that blocking calcium uptake through the slow voltage-sensitive calcium channels during potassium depolarization blocks the mechanical response of the muscle. Thus extracellular calcium ions are required for the excitation-contraction (E-C) coupling during depolarization contractures. On the other hand, electrically evoked twitches were not affected by nitrendipine; therefore, extracellular calcium ions entering via the slow voltage-sensitive channels are not required for E-C coupling during the twitch.
authors.affiliation: Department of Pharmacology, University of Alberta, Edmonton, Canada.
authors.forename: G B
authors.initials: GB
authors.lastname: Frank
authors.forename: L
authors.initials: L
authors.lastname: Konya
authors.forename: T S
authors.initials: TS
authors.lastname: Sudha
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D005071:Evoked Potentials; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009568:Nitrendipine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009568:Nitrendipine; D011188:Potassium