Effects of BAY K 8644, nifedipine, and low Ca2+ on halothane and caffeine potentiation.
The purpose of this investigation was to examine the effects of the Ca2+ agonist BAY K 8644 and the Ca2+ antagonist nifedipine on halothane- and caffeine-induced twitch potentiation of mammalian skeletal muscle. Muscle fiber bundles were taken from normal Landrace pigs and exposed to BAY K 8644 (10 microM), nifedipine (1 microM), and low Ca2+ media administered alone and in combination with halothane (3%) or with increasing concentrations of caffeine (0.5-8.0 mM). Both BAY K 8644 and halothane potentiated twitches by approximately 80%; when they were administered in combination, twitch potentiation was nearly double that caused by either drug alone. In the presence of nifedipine, halothane increased twitches by less than 30%. Low Ca2+ significantly depressed twitches by approximately 25% but also inhibited halothane's inotropic effect. BAY K 8644 augmented caffeine potentiation but only at low caffeine concentrations (0.5-2.0 mM). Nifedipine and low Ca2+ failed to inhibit caffeine's inotropic effects. These results suggest that halothane potentiates twitches via a mechanism that involves or is influenced by extracellular Ca2+.
Williams
J H
JH
Division of Health, Physical Education, and Recreation, Virginia Polytechnic Institute and State University, Blacksburg 24061.
Holland
M
M
Lee
J C
JC
Ward
C W
CW
Davy
K P
KP
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D004357:Drug Synergism; D006221:Halothane / Q000494:pharmacology*; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology*; D013552:Swine
D002110:Caffeine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D002118:Calcium; D006221:Halothane