AJP - Heart and Circulatory Physiology, Vol 253, Issue 5 1141-H1147, Copyright © 1987 by American Physiological Society
Force-length dependence of arterial lamellar, smooth muscle, and myofilament orientations
J. G. Walmsley and R. A. Murphy
Department of Pharmacology, University of Vermont College of Medicine, Burlington 05405.
Force generation by contractile elements of arterial tissue can be affected
by alterations in their alignment with shortening. The orientation and
morphometry of smooth muscle (SM) myofilaments, medial lamellae, and
elastic laminae were examined as a function of length in intact swine
carotid arteries or strips. Intimal-medial tissue strips were fixed during
isometric contractions at lengths (L) defined with respect to the optimal
length for force generation (Lo). The average orientation of SM cells in
two perpendicular planes remained parallel to the long axis of the tissue
at all lengths, but the absolute value of angular deviations increased with
shortening. Tissue lengthening was associated with decreased folding of the
elastic laminae. This decrease in waviness was quantified by a stretch
index (SI). Ultrastructural observations indicated that the myofilament
absolute angular deviation was greater than that for the cellular
alignment. For arteries fixed in situ while constricted, SI was least in
the periintimal laminae and increased in the peripheral laminae. The
average decrease in force-generating capacity on shortening from Lo to 0.6
Lo attributed to increasing SM and myofilament angular deviations was
calculated to be 7%.
