Potentiation of smooth muscle contractility following rapid changes
in isotonic force.
Meiss, Richard A.
Indiana University School of Medicine, Depts. of Physiology and
Biophysics and OB/GYN, Indianapolis, Indiana 46202
APStracts 3:0039C, 1996.
The sudden application of step-increases in afterload (0.4 to 3.0 sec
in duration) arrested the isotonic shortening of electrically
-stimulated ovarian ligament smooth muscle strips from rabbits. Force
steps were chosen to produce, after initial rapid yielding, a quasi
-steady-state in which muscle length and force remained constant.
Removal of the extra afterload allowed renewed shortening that began
with a velocity transiently greater than that measured prior to the
force step (at the same muscle length). The rate of force
redevelopment was also transiently potentiated under isometric
conditions after the removal of the extra load. Both types of
potentiation depended upon force step duration, and the transients
decayed exponentially with a time constant of about 0.25 sec. The
stiffness of the muscle during the force step was initially
depressed, but then increased along an exponential time course while
force and length remained constant. These observations are consistent
with an initial detachment of a portion of the crossbridge array,
which then reattached during the course of the force step, with
potentiation being due either to a transient increase in cycling rate
or to a time-dependent reconfiguration of cytoskeletal elements
supporting the contractile system.
Received 27 March 1995; accepted in final form 17 January 1996.
APS Manuscript Number C172-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96