Journal of Applied Physiology, Vol 71, Issue 2 721-726, Copyright © 1991 by American Physiological Society
Effects of BAY K 8644, nifedipine, and low Ca2+ on halothane and caffeine potentiation
J. H. Williams, M. Holland, J. C. Lee, C. W. Ward and K. P. Davy
Division of Health, Physical Education, and Recreation, Virginia Polytechnic Institute and State University, Blacksburg 24061.
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+.
