Multiple effects of BAY K 8644 and nifedipine on isolated diaphragmatic fibers in vitro.
The dose-response effects of BAY K 8644 and nifedipine on diaphragmatic contractility were assessed in vitro. Isolated diaphragmatic fibers were obtained from rats and placed in an open-topped channel of a Plexiglas tissue chamber perfused with continuously flowing Krebs solution heated to 37 degrees C. Isometric twitch force, generated in response to 1-Hz supramaximal electrical stimulation (4 times/min), was measured with a highly sensitive photoelectric force transducer. Low doses of BAY K 8644 or nifedipine (10(-7) M) were without effect on twitch tension. For 10(-6) M, twitch tension increased by 10 +/- 1% (P less than 0.005) for both drugs. For 10(-5) M, twitch tension increased by 12 +/- 1% (P less than 0.05), and maximal contractures were observed (BAY K 8644 and nifedipine). Simultaneous drug administration did not reveal mutual antagonism as expected; instead the effects were additive, with twitch tension increasing by 30 +/- 2% (P less than 0.001) for 10(-5) M BAY K 8644 + nifedipine. Both BAY K 8644 and nifedipine altered twitch characteristics. In low-calcium media (0.5 mM) twitch potentiation produced by the two drugs was further enhanced (increasing 60% for 10(-5) M BAY K 8644 or nifedipine). Contractures, by contrast, were abolished. From these results it is difficult to reconcile a unique action of these drugs on calcium channels as is conventionally accepted.
Viires
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N
Laboratoire de Pathologie Expérimentale, Institut National de la Santé et de la Recherche, Médicale U 226, Faculté Xavier Bichat, Paris, France.
Pavlovic
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D
Aubier
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M
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D003964:Diaphragm / Q000187:drug effects*; D004357:Drug Synergism; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009543:Nifedipine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D002118:Calcium