Stiffness and contractile properties of avian normal and dystrophic muscle bundles as measured by sinusoidal length perturbations

Abstract

Both tension and stiffness as a function of muscle length were measured under relaxing conditions on isolated small bundles of chemically skinned myofibers from normal and dystrophic chicken pectoral muscles. It was shown that the dystrophic muscle was stiffer than normal muscle and developed more tension for the same amount of stretch. A fraction of stiffness was not removed by extraction with either 0.6 M KI or with 5 M guanidine HCl mixed with 1% mercaptoethanol. The stiffness of dystrophic muscle was also unaffected by treatment with bacterial collagenase under conditions that destroyed the stiffness of tendon. Nyquist plots of normal and dystrophic muscles during calcium-activated isometric contraction were very similar and were characteristic of fast-twitch muscle, as evidenced by three clear exponential processes. The normal appearance of the Nyquist plot of dystrophic muscle demonstrates that cross-bridge function is not altered, and the characteristic slowing of contraction and relaxation is not a consequence of a fast-to-slow transformation of muscle types. The increased stiffness of dystrophic muscle may be a very fundamental change in the biomechanics of dystrophy. We postulate that the stiffness is mediated by an altered form of collagen, which is collagenase-resistant by virtue of excessive crosslinking.

Role of MgATP and MgADP in the cross-bridge kinetics in chemically skinned rabbit psoas fibers. Study of a fast exponential process (C)

“…These results on skinned fibers and results obtained from solution studies generally showed the rate constants to agree within an order of magnitude, indicating that the steps involved in substrate binding and actomyosin dissociation may not be seriously influenced by the length change (reviewed by Goldman, 1987). Physiological studies primarily used rabbit psoas fibers, but in our experience very similar kinetics were seen in fast twitch skeletal musccles (Kawai and Brandt, 1980;Kawai and Schachat, 1984;Feit et al, 1985).…”

Increased resistance of the collagen in avian dystrophic muscle to collagenolytic attack: Evidence for increased crosslinking

“…In our earlier studies, we observed that the passive length-tension diagram was steeper in pectoral muscles from dystrophic chickens (strain 4 13) and that the stiffness associated with the dystrophic muscle could not be reduced by bacterial collagenase. 3 We also demonstrated that crossbridge function was riot impaired in this form of muscular dystrophy, and crossbridges exhibited normal kinetics associated with the fast-twitch fibers. 3 We hypothesized t.hat.…”

“…3 We also demonstrated that crossbridge function was riot impaired in this form of muscular dystrophy, and crossbridges exhibited normal kinetics associated with the fast-twitch fibers.3 We hypothesized t.hat. collagen in the dystrophic muscle is more extensively crosslinked than normal so as to be inaccessible to collagenase.…”

Caveolin-3: A Causative Process of Chicken Muscular Dystrophy

“…This process was energy-independent and caused release of cavins from the caveolae, raising the possibility that cavins may act as cytosolic signals for changes in membrane tension [95]. Feit et al (1985 and measured both tension and stiffness as a function of muscle length under relaxing conditions on isolated small bundles of chemically skinned pectoralis myofibers from normal and dystrophic chickens aged between 45 and 55 days. They indicated that dystrophic pectoralis muscles show increased proportions of high-molecular-weight collagen, suggestive of increased cross-linking and are stiffer than normal muscles, and develop more tension for the same amount of stretch [96,97].…”