Muscle mechanical properties

Inside the typical smooth muscle cell, the cytoplasmic filaments course around the nuclei filling most of the cytoplasm between the nuclei and the plasma membrane. There are two filamentous systems in the smooth muscle cell which run lengthwise through the cell. The first is the more intensively studied actin-myosin sliding filament system. This is the system to which a consensus of investigators attribute most of the active mechanical properties of smooth muscle. It will be discussed in detail below. The second system is the intermediate filament system which to an unknown degree runs in parallel to the actin-myosin system and whose functional role has not yet been completely agreed upon. The intermediate filaments are so named because their diameters are intermediate between those of myosin and actin. These very stable filaments are functionally associated with various protein cytoarchitectural structures, microtubular systems, and desmosomes. Various proteins may participate in the formation of intermediate filaments, e.g., vimentin. 

The analytic validity of an abstract parallel elastic component rests on an assumption. On the basis of its presumed separate physical basis, it is ordinarily taken that the resistance to stretch present at rest is still there during activation. In short, it is in parallel with the filaments which generate active force. This assumption is especially attractive since the actin-myosin system has no demonstrable resistance to stretch in skeletal muscle. However, one should keep in mind, for example, that in smooth muscle cells there is an intracellular filament system which runs in parallel with the actin-myosin system, the intermediate filament system composed of an entirely different set of proteins, (vimentin, desmin, etc.), whose mechanical properties are essentially unknown. Moreover, as already mentioned, different smooth muscles have different extracellular volumes and different kinds of filaments between the cells. 

However, by carrying out experiments with skinned fibers, the composition of the solution surrounding the myofibrils can be controlled and the mechanical properties of the muscle fiber can be related more easily to the biochemistry of force... 

Another example was done by Opitz et al. They utilized P4HB scaffolds to produce viable ovine blood vessels, and then implanted the blood vessels in the systemic circulation of sheep. Enzymatically derived vascular smooth muscle cells (vSMC) were seeded on the scaffolds both under pulsatile flow and static conditions. Mechanical properties of bioreactor-cultured blood vessels which were obtained from tissue engineering approached those of native aorta. 

Modern representations of the virtual heart, therefore, describe structural aspects like fibre orientation in cardiac muscle, together with the distribution of various cell types, active and passive electrical and mechanical properties, as well as the coupling between cells. This then allows accurate reproduction of the spread of the electrical wave, subsequent contraction of the heart, and effects on blood pressure, coronary perfusion, etc. It is important to point out, here, that all these parameters are closely interrelated, and changes in any one of them influence the behaviour of all others. This makes for an exceedingly complex system. 

Blinks, J. R., Olson, C. B., Jewell, B. R., and Braveny, P., Influence of caffeine and other methyxanthines on mechanical properties of isolated mammalian heart muscle, Circ Research, 30, 367, 1972. 

Buspirone is an extremely specific drug that could possibly represent a new chemical class of anxiolytics—azaspirones. As an anxiolytic, its activity is equal to that of benzodiazepines however, it is devoid of anticonvulsant and muscle relaxant properties, which are characteristic of benzodiazepines. It does not cause dependence or addiction. The mechanism of its action is not conclusively known. It does not act on the GABA receptors, which occurs in benzodiazepine use however, it has a high affinity for seratonin (5-HT) receptors and a moderate affinity for dopamine (D2) receptors. Buspirone is effective as an anxiolytic. A few side effects of buspirone include dizziness, drowsiness, headaches, nervousness, fatigue, and weakness. This drug is intended for treatment of conditions of anxiety in which stress, muscle pain, rapid heart rate, dizziness, fear, etc. are observed in other words, conditions of anxiety not associated with somewhat common, usual, and everyday stress. Synonyms for buspirone are anizal, axoren, buspar, buspimen, buspinol, narol, travin, and others. 

In contrast, through eons of evolution Nature has come up with many biopolymers that can combine important mechanical properties including strength, toughness, and elasticity. For example, sUks (Oroudjev et al. 2002), cell adhesion proteins (Law et al. 2003), and connective proteins existing in both soft and hard tissues such as muscle (Kellermayer et al. 1997 Rief, Gautel, et al. 1997 Marszalek et al. 1999 Li et al. 2000), seasheUs (Smith et al. 1999), and bone (Thompson et al. 2001)... 

Huxley, A. F., and Simmons, R. M. (1971a). Mechanical properties of the cross-bridges of frog striated muscle./. Physiol. 218, 59P-60P. 

Phillips, G. N., and Chacko, S. (1996). Mechanical properties of tropomyosin and implications for muscle regulation. Biopolymers 38, 89-95. 

We have discussed the mechanical properties of macromolecules and tissues and introduced the concept of viscoelasticity and the complexity that is introduced by this type of behavior. Although the components of ECMs are limited to cells, ions, water, collagen and elastic fibers, proteoglycans, and smooth muscle, the variation in arrangement of these components leads to wide variation in the mechanical properties of these tissues. It is important to understand the physical basis for the mechanical behavior of tissues. This is a complex task because of the time dependence as well as variations by which the components are attached. Below we attempt to address the physical basis of the mechanical behavior. 

M. G. M. Pryor. Pro. Biophys, and Biophys. Chem. 1, 216-68 (1950). Mechanical properties of protein fibers, muscles. 

Christensen, M., P. P. Pnrslow, and L. M. Larsen. 2000. The effect of cooking temperature on mechanical properties of whole meat, single muscle fibres and perimysial connective tissue. Meat Science 55 301-307. 

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