AJP - Cell Physiology, Vol 248, Issue 5 520-C526, Copyright © 1985 by American Physiological Society
Subcontracture depolarizations increase sarcoplasmic ionized calcium in frog skeletal muscle
K. W. Snowdowne
The hypothesis that the sarcoplasmic concentration of ionized calcium (Cai)
of frog skeletal muscle may control its rate of metabolism was examined by
monitoring the changes in Cai due to perturbations that are known, from the
work of previous investigators, to alter the rate of metabolism. Cai was
measured with aequorin, which was microinjected into isolated fibers in
sufficient quantity to detect basal Cai. When these fibers were exposed to
5-18 mM KCl, 75 mM RbCl2, or 100 mM CsCl2, there was an increase in the
aequorin signal. The potassium-evoked increase in the aequorin signal was
diminished by an increase in the extracellular concentration of Ca or by
Ca-free media containing 3.6 mM Mg, Mn, Sr, or Zn but was enhanced by
subcontracture concentrations of caffeine or media containing nitrate
instead of chloride. These results are consistent with the hypothesis that
Cai may control the rate of metabolism in frog skeletal muscle fibers.
