Journal of Applied Physiology, Vol 60, Issue 3 935-941, Copyright © 1986 by American Physiological Society
Verapamil and zero Ca2+ alter responses of cat muscle to halothane and caffeine
P. A. Deuster, E. L. Bockman, H. Biscardi and S. M. Muldoon
Strips of soleus (slow twitch, oxidative) and gracilis (fast-twitch,
glycolytic) muscle were obtained from 27 anesthetized cats and mounted in
organ baths filled with oxygenated Krebs-Ringer solution (37 degrees C).
The responses to caffeine, halothane (1%), caffeine in the presence of
halothane, and electrical stimulation in the presence of halothane were
examined in the two fiber types. These responses were compared with those
observed in paired strips of muscle that had been treated with verapamil
(10 or 28 microM), a slow calcium (Ca2+) channel blocker, with zero Ca2+,
or with zero Ca2+ where magnesium (3.7 mM Ca2+) was added to replace the
Ca2+. Halothane-induced contractures in the soleus were blocked by
verapamil and zero Ca2+. Caffeine-induced contractures and tetanic
contractions were attenuated in zero Ca2+ and by verapamil in both fiber
types. Halothane overcame verapamil-induced reductions of caffeine
contractures and tetanic contractions in both fiber types. In contrast,
halothane did not overcome zero Ca2+-induced reductions in caffeine
contractures or tetanic contractions in either fiber type. Furthermore, the
addition of Mg2+ to the zero Ca2+ did not restore the responses. The
findings with verapamil indicate that in cat muscle, both halothane- and
caffeine-induced contractures and tetanic contractions are dependent on the
influx of extracellular Ca2+. This extracellular Ca2+ may enter through the
slow Ca2+ channels. However, because halothane in combination with caffeine
or electrical stimulation overcame the effects of verapamil, there may be
other sites involved.
