AJP - Heart and Circulatory Physiology, Vol 257, Issue 5 1573-H1580, Copyright © 1989 by American Physiological Society
Stimulus-specific changes in mechanical properties of vascular smooth muscle
F. V. Brozovich and K. G. Morgan
Department of Medicine, Harvard Medical School, Beth Israel Hospital, Boston, Massachussetts 02215.
To determine whether the mechanical properties of vascular smooth muscle
are stimulus specific, force, stiffness, and the unloaded shortening
velocity (Vmax) were measured during contractions of aortic smooth muscle
strips stimulated with phenylephrine or KCl. After activation, muscle force
and stiffness rose to a steady-state plateau where they were maintained. In
phenylephrine contractions, Vmax peaked during force development and then
fell to a lower steady-state level during force maintenance, whereas in the
KCl contractions, Vmax did not decline during sustained contractions.
Stimulation with KCl, compared with phenylephrine, produced lower
steady-state forces. One possible interpretation is that the muscle formed
latch cross-bridges during phenylephrine contractions, but not during KCl
depolarizations. The slope of the plot of relative muscle force vs.
stiffness for phenylephrine contractions, compared with KCl
depolarizations, was reduced. This may imply tht the relative force per
attached latch crossbridge could be reduced.
