Changes in Striated Muscle Fibres During Contraction and Growth with Particular Reference to Myofibril Splitting

1971 ◽  
Vol 9 (1) ◽  
pp. 123-137
Author(s):  
G. GOLDSPINK
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Actin Filaments ◽  
Sarcomere Length ◽  
Biceps Brachii ◽  
Hexagonal Lattice ◽  
Muscle Fibres ◽  
Cross Sectional ◽  
Tension Development ◽  
Transverse Tubular System ◽  
Myosin Filaments

Ultrastructural measurements were carried out on the mouse biceps brachii and soleus muscles fixed at different states of contraction and stretch. At a sarcomere length of 2.7-2.9 µm the more peripheral actin filaments ran slightly obliquely from the Z-disk to the A-band. This is due to a mismatch between the rhombic actin lattice at the Z-disk and the hexagonal lattice at the M-line. For a perfect transformation of a rhombic lattice into a hexagonal lattice the ratio of the lattice spacings has to be 1:1.51. However, at this sarcomere length the ratio is about 1:2.0 (Z:M). During contraction the angle of the peripheral actin filaments remains approximately the same because the expansion of the M lattice is compensated for, partly by an increase in the Z-lattice spacing and partly by the bowing of the peripheral myosin filaments. When the sarcomeres are stretched beyond 3.0 µm the myosin filaments straighten out and the Z:M ratio decreases. The ratio of 1:1.51 is almost attained when there is no overlap of the actin and myosin filaments. Ultrastructural measurements were also carried out on biceps brachii muscles of different ages. The lattice spacings for a standard sarcomere length did not change during the post-natal growth period. The amount of myofibrillar material and sarcoplasmic reticulum plus transverse tubular system were estimated using linear analysis for muscles at 3 different stages of growth. It was found that the myofibrillar cross-sectional area in an individual muscle fibre may increase 40-fold during growth and that the transverse tubular and sarcoplasmic reticulum systems increase at about the same rate. In both the biceps brachii and the soleus muscles the myosin and actin filaments are not built into a continuous mass but they are divided into numerous discrete myofibrils. Subdivision of the myofibril mass occurs because the myofibrils split once they attain a certain size. The evidence presented in this paper supports the suggestion that the longitudinal splitting of the myofibrils occurs by the ripping of the Z-disks. When tension is rapidly developed by 2 adjacent sarcomeres a stress is produced at the centre of the Z-disk resulting from the oblique pull of the actin filaments. This causes some of the Z-disk filaments to rip and the rip then extends across the disk with the direction of the weave of the lattice. Evidence for the mechanism includes electron-micrographs showing Z-disks that are apparently just commencing to split; in these cases a hole can be seen in the centre of the disk. A model experiment is described which demonstrates the importance of the rate of tension development in causing myofibril splitting. Rapid tension development produces a snatch effect which causes the Z-disk filaments to break more readily. This may explain why the myofibrils in fast muscles tend to be small and discrete whilst those in slow muscles are larger and more irregular in shape.

Sarcoplasmic reticulum function in determining atrioventricular contractile differences in rat heart

1997 ◽  
Vol 273 (5) ◽  
pp. H2498-H2507 ◽  
Author(s):  
Ave Minajeva ◽  
Allen Kaasik ◽  
Kalju Paju ◽  
Enn Seppet ◽  
Anne-Marie Lompré ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Time Course ◽  
Ventricular Myocardium ◽  
Lower Amount ◽  
Functional Coupling ◽  
Cross Sectional ◽  
Tension Development ◽  
Rest Periods ◽  
Tissue Homogenates ◽  
Tension Transients

The relationships between the contractile characteristics and the sarcoplasmic reticulum (SR) function of rat atrial and ventricular trabeculae were compared. The isometric developed tension (DT) and the rates of contraction (+dT/d t) and relaxation (−dT/d t) normalized to cross-sectional area were 3.7, 2.2, and 1.8 times lower, respectively, in intact atrial strips compared with ventricular strips, whereas +dT/d t and −dT/d t(normalized to DT) were 2.3 and 2.8 times higher, respectively, in atria. Atria exhibited a maximal potentiation of DT after shorter rest periods than ventricles and a lower reversal for prolonged rest periods. Caffeine-induced tension transients in saponin-permeabilized fibers suggested that the Ca2+concentration released in atrial myofibrils reached a lower maximum and decayed more slowly than in ventricular preparations. However, the tension-time integrals indicated an equivalent capacity of sequestrable Ca2+ in SR from both tissues. In atrial, as in ventricular myocardium, the SR Ca2+ uptake was more efficiently supported by ATP produced by the SR-bound MM form of creatine kinase (CK; MM-CK) than by externally added ATP, suggesting a tight functional coupling between the SR Ca2+adenosinetriphosphatase (ATPase) and MM-CK. The maximal rate of oxalate-supported Ca2+ uptake was two times higher in atrial than in ventricular tissue homogenates. The SR Ca2+-ATPase 2a mRNA content normalized to 18S RNA was 38% higher in atria than in ventricles, whereas the amount of mRNA encoding the α-myosin heavy chain, calsequestrin, and the ryanodine receptor was similar in both tissues. Thus a lower amount of readily releasable Ca2+ together with a faster uptake rate may partly account for the shorter time course and lower tension development in intact atrial myocardium compared with ventricular myocardium.

Band Patterns in Chick Muscle at Short Sarcomere Length

1970 ◽  
Vol 28 ◽  
pp. 144-145
Author(s):  
M. Hagopian ◽  
D. Spiro ◽  
P. Yau
Keyword(s):  
Electron Microscopy ◽  
Actin Filaments ◽  
Sarcomere Length ◽  
Pectoral Muscle ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Contraction Band

Glycerinated chick pectoral muscle was prepared for electron microscopy. Sarcomere lengths varied from 2.3 to 1.1μ reflecting various degrees of shortening. Over a sarcomere range of 2.3 to 1.3μ the thin actin filaments which measure 1.0μ and the thick myosin filaments which measure 1.5μ are constant in length (Fig. 1). At sarcomere lengths below 2μ the thin filaments penetrate through the center of the A band into the opposite halves of the sarcomere producing A contraction bands as previously described. In sarcomeres which measure 1.5 to 1.3μ additional contraction bands are noted adjacent to the Z lines. In longitudinal sections the array of filaments in the Z contraction band appears orderly (Fig. 2). It is our impression that these Z contraction bands result from penetration of the tapered lateral ends of the myosin filaments through the Z lines into the adjacent sarcomere rather than a crumpling of thick filaments as has been previously stated. Below 1.3μ in length the sarcomeres are disorganized, and it is not possible to define filament lengths.

The Effects of Immobilization, after Lower Leg Fracture, on the Contractile Properties of Human Triceps Surae

1984 ◽  
Vol 66 (3) ◽  
pp. 277-282 ◽  
Author(s):  
M. J. White ◽  
C. T. M. Davies
Keyword(s):  
Lower Leg ◽  
Voluntary Contraction ◽  
Contractile Properties ◽  
Triceps Surae ◽  
Anthropometric Measurement ◽  
Muscle Fibres ◽  
Type I ◽  
Cross Sectional ◽  
Tension Development ◽  
Lower Leg Fracture

1. The contractile properties of the triceps surae were evaluated in 11 patients after unilateral fracture of the lower leg and subsequent immobilization for 135 ± 68 days. Calf muscle cross-sectional area (plus bone: CSA) was assessed from anthropometric measurement. 2. It was shown that the injured leg had a faster time to peak tension and increased half-relaxation time (1/2RT); twitch force (Pt) was reduced by 25%. Evoked maximal tetanic tensions (P0) at 10 and 20 Hz were reduced by 51% and 46% respectively compared with the uninjured leg. The force of a maximal voluntary contraction (MVC) was also reduced, by 50%, but calf circumference and CSA were only 5% and 16% respectively lower in the injured leg. 3. It was concluded that the changes in contractile speed may indicate a relatively greater atrophy of slow (type I) muscle fibres. 4. The relationship between CSA and tension generation in the injured limb was shown to be poor after immobilization and during recovery. Anthropometric estimation of CSA does not appear to reflect the degree of muscle wasting, as indicated by reduced tension development after immobilization.

The effect of selection for altered body weight on the ultrastructural components of skeletal muscle fibres

1983 ◽  
Vol 36 (2) ◽  
pp. 223-227
Author(s):  
A. C. B. Hooper ◽  
M. P. Hurley
Keyword(s):  
Body Weight ◽  
Biceps Brachii ◽  
Muscle Growth ◽  
Cross Sectional Area ◽  
Muscle Fibres ◽  
Sectional Area ◽  
Weight Changes ◽  
Cross Sectional ◽  
Microscopic Studies ◽  
Selection For

ABSTRACTUltrastructural parameters of muscle growth were measured in lines of mice which had undergone 15 generations of selection for high and low body weight. Previous light microscopic studies of these lines had shown that selection for altered body weight evokes correlated responses in the weight of skeletal muscles as a result of changes in both the number and the longitudinal and transverse dimensions of the fibres.The length of the myosin filaments and of the actin filaments (including the Z disc) did not differ significantly from the controls in the mm. sternomastoideus, biceps brachii and tibialis anterior of mature male mice from the two selection lines. The mean cross-sectional area of the myofibrils of the mm. sternomastoideus and biceps brachii were also unaltered by selection for high and low body weight. Changes in the area of the fibres were brought about by increases and decreases in the number of their constituent myofibrils and corresponding changes in the non-contractile elements.Selection for high and low body weight did not affect the dimensions of the contractile elements of the muscle fibres. The genetically determined alterations in the length and cross-sectional area of the fibres were due to changes in the number of their constituent sarcomeres and myofibrils. These changes are similar to those which occur during growth.

The Ultrastructure of the White Striated Myotomal Muscle of the Cod, Gadus morhua

1967 ◽  
Vol 24 (12) ◽  
pp. 2549-2553 ◽  
Author(s):  
C. M. Bishop ◽  
P. H. Odense
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cross Section ◽  
Actin Filaments ◽  
Gadus Morhua ◽  
Striated Muscle ◽  
Fish Muscle ◽  
Transverse Tubular System ◽  
Tubular System ◽  
Myotomal Muscle

The structure of the white skeletal muscle of the cod (Gadus morhua) is described. The peripheral fibrils are ribbon-like and rectangular in cross section with the long axis normal to the sarcolemma. The inner fibrils are mainly polygonal in cross section. Most of the mitochondria and nuclei are peripheral to the fibrils and next to the sarcolemma. The arrangement of the contractile proteins is typical for striated muscle, and the sarcoplasmic reticulum and transverse tubular system are similar to those in other white skeletal fish muscle. A distinct N-band is apparent with indications of branching and reorientation of the actin filaments. Mitochondria are often closely associated with the Z line.

Sarcomere Length During Post-Natal Growth of Mammalian Muscle Fibres

1968 ◽  
Vol 3 (4) ◽  
pp. 539-548
Author(s):  
G. GOLDSPINK
Keyword(s):  
Sarcomere Length ◽  
Biceps Brachii ◽  
Muscle Length ◽  
Muscle Fibres ◽  
Biceps Brachii Muscle ◽  
Newborn Animal ◽  
Maximum Tension ◽  
Mammalian Muscle ◽  
Extended Position ◽  
The Difference

The length of the sarcomeres, the A- and the 1-filaments and their percentage overlap were measured in the fibres of the biceps brachii muscle from mice of different ages. The sarcomere length with the limb in the fully extended position was found to increase from 2.3 µ in the newborn animal to 2.8 µ in the adult. This increase was due to a decrease in the percentage overlap of the filaments and not to any change in the filament lengths. The sarcomeres at the ends of the fibres were found to be shorter than those in the middle of the muscle, at all ages. When the muscles were stretched beyond their resting length, only about the middle 60 % of the sarcomeres in the young muscles increased in length. Length/tension plots were obtained for young and old muscles and the difference in the shape of these plots could be explained as being due to the non-functional terminal sarcomeres of the young muscles. The maximum tension developed by the young muscles was found to be attained at an initial muscle length about 10 % greater than their length at maximum limb extension. The adult muscles developed maximum tension at their length at maximum limb extension.

The Fibrillar Flight Muscles of Giant Water-Bugs: An Electron-Microscope Study

1967 ◽  
Vol 2 (3) ◽  
pp. 435-444
Author(s):  
DOREEN E. ASHHURST
Keyword(s):  
Electron Microscope ◽  
Sarcoplasmic Reticulum ◽  
Flight Muscle ◽  
Muscle Fibres ◽  
Transverse Tubular System ◽  
Tropical Water ◽  
Tubular System ◽  
Flight Muscles ◽  
And Function ◽  
Water Bugs

The fibrillar flight muscles of several species of tropical water-bugs of the family Belostomatidae have been examined in the electron microscope. The myofibrils are very similar to those of the other fibrillar flight muscles which have been studied. The membrane systems, however, display features which appear to be peculiar to this family. The sarcoplasmic reticulum can be divided into three parts: a series of interconnecting vesicles surrounding the Z-lines, randomly scattered small vesicles around the myofibrils, and flattened cisternae which lie along the transverse tubular system, and form the dyads. These three components of the sarcoplasmic reticulum do not appear to be interconnected. The cisternae of the dyads contain an electrondense substance. The narrow tubules of the transverse tubular system or T-system penetrate deep into the fibre from the cell membrane. They follow a course roughly perpendicular to the myofibrils at the level of the M-lines. The dyads are scattered along their length, and may not be near a myofibril. Another system of very large vesicles is found in the muscle fibres, interspersed among the mitochondria. These vesicles usually appear to be empty; their nature and function are not at present known. Numerous mitochondria are present among the myofibrils. The peculiarities of the water-bug fibrillar flight muscle are discussed in relation to the flight muscles of other insects and the physiological properties of fibrillar flight muscle.

Electron-microscopic structure of denervated skeletal muscle

1969 ◽  
Vol 174 (1035) ◽  
pp. 253-269 ◽  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibres ◽  
Microscopic Structure ◽  
Sectional Area ◽  
Rat Diaphragm ◽  
Denervated Muscle ◽  
Electron Microscopic ◽  
Cross Sectional ◽  
Myosin Filaments ◽  
Filament Spacing

(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.

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