AJP - Cell Physiology, Vol 233, Issue 1 47-C55, Copyright © 1977 by American Physiological Society
Mechanical properties of taenia coli smooth muscle in spontaneous contraction
J. M. Price, P. Patitucci and Y. C. Fung
The following mechanical tests have been performed on spontaneously
contracting taenia coli: isometric step stretch, isotonic step loading, and
length-tension. Passive stress-strain tests have also been done.
Information on spontaneous contraction was more readily obtained in
isometric tests. In length-tension tests, each isometric contraction was
analyzed on a phase plane which is a representation of muscle stress,
sigma(t), versus the rate of change of stress, sigma(t). The curve in the
phase plane provided parameters for describing spontaneous contraction as a
function of muscle length, L. The maximum active stress in a cycle of
spontaneous contraction, S(L)max, and the maximum rate of increasing active
stress, [S(L)]max, were shown to depend on L in the same way. Both
parameters attain a maximum value (upper bound) at the same muscle length,
Lmax. When L less than Lmax, the minimum stress in a spontaneous
contraction, sigma(l)min, is negligible. If L greater than Lmax,
sigma(L)min increases nonlinearly and is equal to the passive stress,
tau(L), in an epinephrine-relaxed muscle. The results show that the ratio
of [S(L)]max to S(L)max, eta(L), is constant for a physiological range of
muscle length. This suggests that eta(L) may be used as an index of
contractility for taenia coli.
