The Journal of General Physiology, Vol 80, 191-202, Copyright © 1982 by The Rockefeller University Press
Intracellular Ca release in skinned smooth muscle
K Saida
The release of internal Ca from saponin-treated skinned smooth muscle of
guinea pig taenia caecum was studied. The amount of Ca released was
estimated by the area under the contraction curve during treatment with 25
mM caffeine in the presence of 0.1 mM EGTA. The magnitude of the caffeine
response in skinned muscle, after loading with 10(-6) M Ca for 3 min, was
similar to that in the depolarized muscle in the presence of EGTA before
treatment with saponin. This suggests that Ca in the skinned muscle was in
a physiological range after loading. The release of Ca from the storage
site could be facilitated by Ca itself when the skinned muscle was exposed
to Ca above 3 x 10(-6) M. An increase in environmental MG concentration
suppressed the Ca-induced Ca release mechanism. Sudden replacement of
propionate with Cl in the bathing solution made it possible to release Ca
from the storage site. This "depolarization"-induced Ca release occurred
only immediately after the application of Cl; thereafter, the Ca release
mechanism seemed to be inactivated by the prolonged presence of Cl. These
results suggest that two mechanisms of Ca release operate in smooth muscle:
(a) release induced by Ca itself, and (b) release by "depolarization".
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