Mechanisms for the mechanical plasticity of tracheal smooth muscle. Gunst, Susan J., Richard A. Meiss, Ming-Fang Wu, Michael Rowe. Dept. of Physiology and Biophysics, Indiana Univ. School of Medicine, Indianapolis, IN, 46202, Telephone: 317 274-4108, FAX: 317 274-3318
APStracts 2:0040C, 1995.
In smooth muscle tissues, the relationship between muscle or cell length and active force can be modulated by altering the cell or tissue length during stimulation. Mechanisms for this mechanical plasticity were investigated by measuring muscle stiffness during isometric contractions in which contractile force was graded by changing stimulus intensity or muscle length. Stiffness was significantly higher in contracted than in resting muscles at comparable forces; however, the relationship between stiffness and force during force development was curvilinear and independent of muscle length and stimulus intensity. This suggests that muscle stiffness during force development reflects properties of cellular components other than crossbridges which contribute to the series elasticity only during activation. During the tonic phase of isometric contraction, muscle stiffness increased while force remained constant. A step decrease in the length of a contracted muscle resulted in a high level of stiffness relative to force during isometric force redevelopment following the length step. We propose that the arrangement of the cytoskeleton can adjust to changes in the conformation of resting smooth muscle cells, but that the organization of the cytoskeleton becomes more fixed upon contractile activation and is modulated very slowly during a sustained contraction. This may provide a mechanism for optimizing force development to the physical conformation of the cell at the time of activation. 

Received 12 September 1994; accepted in final form 23 November 1994
APS Manuscript Number C0546-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.