Skinned muscle fibers

Measurements of metabolite concentrations in muscle fibers before and after fatiguing stimulation have shown that ATP decreases from 6 to 4.6 mM and PCr decreases from 35 to 2.4 mM with a calculated increase in Pj from 3 to 38 mM (Dawson et al., 1978 Nassar-Gentina et al., 1978). The free ADP concentration was calculated to increase from 30 to 200 pM. At the same time pH decreased from 7.0 to 6.5 (Dawson et al., 1978 Juel, 1988 Westerblad and Lannergren, 1988). The effect of these metabolic changes has been studied in skinned muscle fibers, i.e., fibers in which the cell membrane has been removed. The skinning of the fibers... 

This section examined small muscle preparations stimulated electrically or skinned muscle fibers maintained in superfused baths with different substance concentrations. The electrical stimulation was either continuous or intermittent for relatively short durations. 

Godt, R.E. (1981). A simple electrostatic model can explain the effect of pH upon the force-pCa relation of skinned muscle fibers. Biophys. J. 35, 385-392. 

Mitsumoto, FT, Deboer, G. E., Bunge, G., Andrish, J. T., Tetzlaff, J. E., and Cruse, R. P., Fiber type specific caffeine sensitivities in normal human skinned muscle fiber, Anesthesiology, 72, 50, 1990. 

Goblet C, Mounier Y. 1987. Activation of skinned muscle fiber by calcium and strontium ions. Can J Physiol Pharmacol 65 642-647. 

Kerrick WGL, Zot HG, Hoar PE, et al. 1985. Evidence that the Sr2- - activation properties of cardiac troponin C are altered when substituted into skinned muscle fibers. J Biol Chem 260(29) 15687-15693. 

Nakamura, Y, Kobayashi, (., Gilmore, (., Mascal, M Rinehart, K.L(r, Nakamura, H and Ohizumi, Y. (1986) Bromoeudistomin D, a novel inducer of calcium release from fr agmented sarcoplasmic reticulum that causes contractions of skinned muscle fibers. J. Biol. Chem., 261, 4139-4142. 

A skinned fiber is a muscle fiber, the sarcolemma of which has been mechanically removed or which is made freely permeable to small molecules, such as Ca2+, Mg2+, EGTA, ATP, soluble enzymes and others by a chemical agent (saponin, (3-escin or Staphylococcus a-toxin). The organization of the sarcoplasmic reticulum (SR) and myofibrils is kqrt as they are in the living muscle. 

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... 

Nosek, T.M., Fender, K. Y., Godt, R.E. (1987). It is diprotonated inorganic phosphate that depresses force in skinned skeletal muscle fibers. Science 236. 191-193. 

Muscle biopsy is usually undertaken to confirm the provisional clinical diagnosis. Because the skin lesions normally precede those in muscle, biopsies of muscle taken early may show little abnormality. Inflammatory foci may be scanty or absent and muscle fiber diameters may be normal. However typical biopsies show discrete foci of inflammatory cells, with a predominance of B-lymphocytes (see Figure 18). These cells are situated in perimysial connective tissue rather than in the en-domysium and are often also perivascular in location. Muscle fiber necrosis occurs in JDM but muscle fibers do not appear to be the primary target of the disordered immune process. Rather, it is the micro vasculature of the muscle which appears to degenerate first and muscle necrosis is preceded by capillary necrosis, detectable at the ultrastructural level. 

Various syndromes associated with hypereosinophilia involve skeletal muscle. There is a rare form of polymyositis which is characterized by this feature (defined as exceeding 1,500 eosinophils/mm for at least six months). Clinical presentation includes skin changes, heart and lung involvement, and peripheral neuropathy as well as proximal myopathy. The condition must be distinguished from trichinosis and other parasitic infections associated with hypereosinophilia. Muscle biopsy findings are interstitial and perivascular infiltrates in which eosinophils predominate but are accompanied by lymphocytes and plasma cells, and occasional muscle fiber necrosis. Fascitis may also be associated with hypereosinophilia (Shulman s syndrome). This condition is characterized by painful swelling of skin and soft tissues of trunk and extremities and weakness of limb muscles. Biopsy of muscle... 

Endo, M., Tanaka, M., and Ogawa, Y., Calcium induced release of calcium from sarcoplasmic reticulum of skinned skeletal muscle fibers, Nature, 228, 34, 1970. 

Wendt, I. and Stephenson, D., Effects of caffeine on calcium-activated force production in skinned cardiac and skeletal muscle fibers of the rat, European Journal of Physiology, 398, 210, 1983. 

Gregor, M. Mejsnar, J. Janovska, A. Zurmanova, J. Benada, O. Mejsnaro-va, B. Creatine kinase reaction in skinned rat psoas muscle fibers and their myofibrils. Physiol.Res., 48, 27-35 (1999)... 

Most P, Remppis A, Weber C, Bernotat J, Ehlermann P, Pleger ST, Kirsch W, Weber M, Uttenweiler D, Smith GL, Katus HA, Fink RH. 2003c. The C terminus (amino acids 75-94) and the linker region (amino acids 42-54) of the Ca2+-binding protein S100A1 differentially enhance sarcoplasmic Ca2+ release in murine skinned skeletal muscle fibers. J Biol Chem 278(29) 26356-26364. 

A 46-year-old woman, who took clonidine 25 mg bd for menopausal flushing, developed depigmentation and swelling of her forearms (25). A skin biopsy showed a pattern consistent with immune complex disease, with IgG, IgM, Clq, C2c, and C4 complement between muscle fibers and at the dermo-epidermal junctions. All of these abnormalities disappeared after withdrawal. 

In the 1920s, impedance was applied to biological systems, including the resistance and capacitance of cells of vegetables and the dielectric response of blood suspensions. ° Impedance was also applied to muscle fibers, skin tissues, and other biological membranes. " The capacitance of the cell membranes was found to be a function of frequency, and Fricke observed a relationship between the frequency exponent of the impedance and the observed constant phase angle. In 1941, brothers Cole and Cole showed that the frequency-dependent complex... 

Skin contact with petroleum solvents can cause allergic contact dermatitis. Preexisting skin disease may increase the potential for adverse effects. Overexposure via inhalation of petroleum ether affects primarily the CNS. Short-term, high overexposure is associated with an excitatory phase followed by a depressive phase. Exposures of 100-400 ppm for 7h have resulted in headaches, fatigue, and incoordination with dose-associated effects on equilibrium, reaction time, visuomotor coordination, and memory. Inhalation exposures of 445-1250 ppm resulted in blurred vision, a cold sensation in extremities, fatiguability, headache, fatty demylination of muscle fibers, and demylination and mild axonal degeneration. Exposure to 880 ppm produced eye and throat irritation with temporary olfactory fatigue. 

Donaldson SKB, Kerrick WGL. 1975. Characterization of the effects of Mg2+ on Ca2+- and Sr -activatcd tension generation of skinned skeletal muscle fibers. J Gen Physiol 66 427-444. 

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