Number Of Myofibrils Research Articles

Effects of protein synthesis inhibitors on muscle growth in the puparium of Calliphora vomitoria

Methods are described for measuring the length and the myofibril diameter of the sixth dorsal longitudinal flight muscle of 7-, 8- and 9-day old puparia of C. vomitoria. The muscle fibres are divided up into nuclear deliminated areas and the number of myofibrils in one of these areas is found to be constant. The growth of the myofibrils in one of the nuclear deliminated areas is described. Injections of 20 μg of cycloheximide reduces amino acid incorporation into protein to 3–4% of the normal level in 7- and 8-day-old puparia. Injections of cycloheximide does not stop the elongation of the flight muscle but prevents increases in myofibril diameter. These different responses are discussed.

Myocardial ultrastructure in patients with chronic aortic valve disease

Light and electron microscopic observations were made on left ventricular myocardium removed at operation from 16 patients with chronic aortic valve disease. In all 16 patients most cardiac muscle cells were hypertrophid, and surrounded by small amounts of fibrous tissue. In two of the six patients with pure aortic regurgitation and in four of the five patients with combined aortic stenosis and regurgitation, cardiac muscle cells with evidence of degeneration were present in addition to hypertrophied, nondegenerated cells. Degenerated cardiac muscle cells were not observed in the six patients with predominant aortic stenosis. Cardiac muscle cells with mild degeneration showed focal myofibrillar lysis, with preferential loss of thick myofilaments, and focal proliferation of tubules of sarcoplasmic reticulum. More severely degenerated muscle cells showed a marked decrease in the numbers of myofibrils and T tubules and proliferation of sarcoplasmic reticulum or mitochondria, or both. Severely degenerated cells usually were present in areas of marked fibrosis, often were atrophic, had thickened basement membranes and had lost their intercellular connections. These findings suggest that degenerated cardiac muscle cells have poor contractile function and may be responsible for impaired cardiac performance in some patients with chronic aortic valve disease.

Distribution and dimension of the T-system in different muscle fiber types in the atlantic hagfish (Myxine glutinosa, L.).

Triad density relative to sarcomeres, size of T-system tubules, sarcomere length, muscle fiber diameter in native and fixed states, and size of myofibrils were measured in four straited muscle fiber types in Atlantic hagfishes (Myxine glutinosa, L.) of different sizes. Traids occur at A/I-injunctions in all fiber types. The density of traids relative to sarcomeres is higher in "white" than in "red" muscle fibers. The T-tubules show no sign of branching. The area of the T-system tubules is 3-4 times the surface area in 80 mum "white" muscle fibers and 1-2 times that in 60 mum "red" fibers. The size of myofibrils is similar in "white", "intermediate", and "red" fibers of m. parietalis, and constant through a large span of animal size. In "white" fibers, increase in diameter up to 90 mum is accompanied by an increase in the number of myofibrils, not by an increase in the individual size of the myofibrils. Above 90 mum, "white" fibers grow by increasing the amount of intermyofibrillar space. This is reflected by an extensive shrinkage of the thicker "white" fibers during the preparative procedure for electron microscopy, a shrinkage that is limited only by complete packing of the myofibrils. "Red" fibers shrink much less.

Mixed M�llerian tumors of the uterus

In the present study the differentiation of rhabdomyoblasts of two carcinosarcomas of the uterus is analysed electronmicroscopically. During the development of rhabdomyoblasts three cell types can be distinguished: 1. the undifferentiated mesenchymal cell with abundant ribosomes but few other cell organelles. Usually these cells are already associated to each other in strands of 2-4 cells. Occasionally cytoplasmic areas with numerous nonspecific filaments can be observed. 2. the light rhabdomyoblast which is characterized by its conspicuous nonspecific cytoplasmic filaments and its reduction in ribosomes. Specific myofilaments can be visualized only occasionally in this cell type. 3. more differentiated rhabdomyoblasts. These cells can be identified clearly by the presence of large numbers of myofibrils and myofibrillar fragments. Higly organized myofibrils as seen in skeletal muscle are seldom found. Transitional forms between these cell types are also observed. The functions of Z-bodies and of the sarcotubular system in the process of myofibrillar differentiation are discussed.

Congenital Myofibrillar Hypoplasia of Piglets: Ultrastructure of Affected Fibres

SUMMARY By electronwicroscopy, affected fibres of one-day-old pigs with myofibrillar hypoplasia were characterized as having: (a) reduced numbers of myofibrils occupying only a part of the fibre; (b) myofibrils generally smaller than in normal fibres, with some longitudinal splitting of myofibrils and some imperfect alignment of transverse bauds; (c) granular material mainly in two size ranges, with modes of approximately 15 and 30 nm, lying between myofibrils and occupying the remaining free space within fibres. In presumed normal 80-day foetuses there was a similar amount of myofibrillar material, but it was more evenly distributed throughout the fibres and there were comparatively few granules.

Ultrastructural Changes During Development of Myocardial Hypertrophy

Although it has been shown that the myocardial cell may increase in both width and length with hypertrophy, there is little morphologic evidence for the mechanism of this increase in cell size or for the decreased contractility associated with hypertrophied and failing myocardium. It has been suggested that the myocardial cell may increase in size by one or more of three means: 1) an increase in the number of myofibrils, 2) the addition of normal sized filaments to the periphery of already existing myofibrils, or 3) by the addition of new complete sarcomere units to the cell.

Electron-microscopic structure of denervated skeletal muscle.

(1) An electron-microscopic study was made of normal and denervated muscle fibres in the rat diaphragm. (2) Early after denervation muscle fibres become hypertrophic. The cross-sectional area of the fibres and the number of myofibrils within them are increased. Since filament spacing is not significantly altered, it is concluded that during hypertrophy the number of actin and myosin filaments is increased. (3) A few weeks after denervation the muscle fibres are greatly reduced in size. This atrophy is mainly a consequence of two processes: fragmentation of the muscle fibre, with subsequent degeneration of the fragments; and disintegration of myofilaments.

Some observations on the ultrastructure of the hummingbird pectoral muscles.

In the hummingbird, the supracoracoideus, the chief elevator muscle of the wing, though smaller than the depressor muscle pectoralis, is relatively better developed than in other birds. It is also unique in its cellular organization in that it consists of only the red (type 1) fibers like the pectoralis. Both muscles have conspicuously large aggregations of mitochondria which may be so numerous and densely packed in certain areas that the number of myofibrils in the area may be relatively insignificant, a feature hitherto unknown and unparalleled in vertebrate skeletal muscles. Of the two muscles the supracoracoideus appeared to contain larger aggregations of mitochondria, suggesting greater mitochondrial density in that muscle. This finds support in the biochemical observations of earlier investigators that, in hummingbirds, the supracoracoideus has a higher level of succinic dehydrogenase activity than the pectoralis. The ability of the hummingbird for hovering flight is attributed to the above unique features in its pectoral muscles.With the numerous mitochondria and fat droplets interspersed between myofibrils, some myofibrils tend to split and bifurcate. Similar splitting is also seen in regions where there is considerable proliferation of the sarcoplasmic reticulum. Numerous glycogen granules are present within the sarcoplasmic reticulum. Both muscles have copious blood supply through numerous capillaries. The disposition of the myofibrils in relation to the capillaries indicates that muscular pumping should be an effective mechanism for intramuscular transport of oxygen and metabolites.

Effect of exercise on number of myofibrils per fiber in sartorius muscle of the rat.

The number of myofibrils per fiber at seven different cross-sectional levels of the sartorius muscles of exercised rats was compared with the number of myofibrils per fiber of the sartorius muscles of unexercised control animals. No statistically significant differences were observed. The number of myofibrils per fiber in the exercised animals was more variable than in the control animals, and the pattern of distribution suggested increases in the number of myofibrils per fiber at the ends of the muscles.