Natural Variability in the Length of Thin and Thick Filaments in Single Fibres From a Crab, Portunus Depurator

1970 ◽  
Vol 6 (2) ◽  
pp. 559-592
Author(s):  
CLARA FRANZINI-ARMSTRONG
Keyword(s):  
Thick Filament ◽  
Natural Variability ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Striation Spacing ◽  
Free Region ◽  
Cross Striation ◽  
Single Fibres ◽  
Length Changes ◽  
Medium Type

The carpopodite flexor of the walking legs of the crab Portunus depurator contains fibres belonging to 3 groups. These are characterized by differences in the cross-striation spacing. Fibres having sarcomeres of approximately 4, 5 and 7 µm are here called short, medium and long sarcomere types, respectively. Within individual fibres belonging to any of the groups the length of the A band is not constant. Up to 25 % length differences have been measured in A bands belonging even to the same fibril. The bridge-free regions of the thick filaments are not always in the centre, so that the filaments are often asymmetric. Analogally, the L line, resulting from the alignment of the bridge-free regions of the thick filaments, may be asymmetrically placed in the Z band. The length of the bridge-free region in crab thick filaments is 60 nm, while the corresponding region in vertebrate thick filaments is 120 nm. This is discussed in terms of a possible model of the filament. The length of the thin filaments is proportional to that of the thick filaments in the corresponding portion of the sarcomere. When two A bands of different length occur in adjacent positions along the fibril, the Z line is not a centre of symmetry. The ratio of thin to thick filament number is variable in individual fibrils. In general, the ratio is higher in the medium sarcomere type fibres than in the short sarcomere type. Stretched and shorter portions of single fibres of the medium type have been examined and the A-band length populations compared. From such a study it can be deduced that passive length changes occur in crab fibres by sliding of thin and thick filaments.

Myosin thick filament lability induced by mechanical strain in airway smooth muscle

2001 ◽  
Vol 90 (5) ◽  
pp. 1811-1816 ◽  
Author(s):  
Kuo-Hsing Kuo ◽  
Lu Wang ◽  
Peter D. Paré ◽  
Lincoln E. Ford ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Cross Sections ◽  
Structural Changes ◽  
Isometric Force ◽  
Mechanical Strain ◽  
Thick Filament ◽  
Functional Changes ◽  
Thick Filaments ◽  
Length Changes

Airway smooth muscle adapts to different lengths with functional changes that suggest plastic alterations in the filament lattice. To look for structural changes that might be associated with this plasticity, we studied the relationship between isometric force generation and myosin thick filament density in cell cross sections, measured by electron microscope, after length oscillations applied to the relaxed porcine trachealis muscle. Muscles were stimulated regularly for 12 s every 5 min. Between two stimulations, the muscles were submitted to repeated passive ±30% length changes. This caused tetanic force and thick-filament density to fall by 21 and 27%, respectively. However, in subsequent tetani, both force and filament density recovered to preoscillation levels. These findings indicate that thick filaments in airway smooth muscle are labile, depolymerization of the myosin filaments can be induced by mechanical strain, and repolymerization of the thick filaments underlies force recovery after the oscillation. This thick-filament lability would greatly facilitate plastic changes of lattice length and explain why airway smooth muscle is able to function over a large length range.

scholarly journals LOCALIZATION OF MYOSIN FILAMENTS IN SMOOTH MUSCLE

1968 ◽  
Vol 37 (1) ◽  
pp. 105-116 ◽  
Author(s):  
Robert E. Kelly ◽  
Robert V. Rice
Keyword(s):  
Smooth Muscle ◽  
Cross Section ◽  
Striated Muscle ◽  
Thick Filament ◽  
Longitudinal Axis ◽  
Thin Filaments ◽  
Chicken Gizzard ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Muscle Myosin

Thick myosin filaments, in addition to actin filaments, were found in sections of glycerinated chicken gizzard smooth muscle when fixed at a pH below 6.6. The thick filaments were often grouped into bundles and run in the longitudinal axis of the smooth muscle cell. Each thick filament was surrounded by a number of thin filaments, giving the filament arrangement a rosette appearance in cross-section. The exact ratio of thick filaments to thin filaments could not be determined since most arrays were not so regular as those commonly found in striated muscle. Some rosettes had seven or eight thin filaments surrounding a single thick filament. Homogenates of smooth muscle of chicken gizzard also showed both thick and thin filaments when the isolation was carried out at a pH below 6.6, but only thin filaments were found at pH 7.4. No Z or M lines were observed in chicken gizzard muscle containing both thick and thin filaments. The lack of these organizing structures may allow smooth muscle myosin to disaggregate readily at pH 7.4.

scholarly journals Changes in thick filament length in Limulus striated muscle.

1977 ◽  
Vol 75 (2) ◽  
pp. 366-380 ◽  
Author(s):  
M M Dewey ◽  
B Walcott ◽  
D E Colflesh ◽  
H Terry ◽  
R J Levine
Keyword(s):  
Horseshoe Crab ◽  
Striated Muscle ◽  
Thick Filament ◽  
Filament Length ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Wide Range ◽  
The Difference

Here we describe the change in thick filament length in striated muscle of Limulus, the horseshoe crab. Long thick filaments (4.0 microns) are isolated from living, unstimulated Limulus striated muscle while those isolated from either electrically or K+-stimulated fibers are significantly shorter (3.1 microns) (P less than 0.001). Filaments isolated from muscle glycerinated at long sarcomere lengths are long (4.4 microns) while those isolated from muscle glycerinated at short sarcomere lengths are short (2.9 microns) and the difference is significant (P less than 0.001). Thin filaments are 2.4 microns in length. The shortening of thick filaments is related to the wide range of sarcomere lengths exhibited by Limulus telson striated muscle.

scholarly journals Structure and paramyosin content of tarantula thick filaments.

1983 ◽  
Vol 97 (1) ◽  
pp. 186-195 ◽  
Author(s):  
R J Levine ◽  
R W Kensler ◽  
M C Reedy ◽  
W Hofmann ◽  
H A King
Keyword(s):  
Evolutionary Relationship ◽  
Radial Distance ◽  
Thick Filament ◽  
Optical Diffraction ◽  
Thin Filaments ◽  
Biochemical Characteristics ◽  
Thick Filaments ◽  
Cross Bridges ◽  
Centers Of Mass ◽  
Relationship Of

Muscle fibers of the tarantula femur exhibit structural and biochemical characteristics similar to those of other long-sarcomere invertebrate muscles, having long A-bands and long thick filaments. 9-12 thin filaments surround each thick filament. Tarantula muscle has a paramyosin:myosin heavy chain molecular ratio of 0.31 +/- 0.079 SD. We studied the myosin cross-bridge arrangement on the surface of tarantula thick filaments on isolated, negatively stained, and unidirectionally metal-shadowed specimens by electron microscopy and optical diffraction and filtering and found it to be similar to that previously described for the thick filaments of muscle of the closely related chelicerate arthropod, Limulus. Cross-bridges are disposed in a four-stranded right-handed helical arrangement, with 14.5-nm axial spacing between successive levels of four bridges, and a helical repeat period every 43.5 nm. The orientation of cross-bridges on the surface of tarantula filaments is also likely to be very similar to that on Limulus filaments as suggested by the similarity between filtered images of the two types of filaments and the radial distance of the centers of mass of the cross-bridges from the surfaces of both types of filaments. Tarantula filaments, however, have smaller diameters than Limulus filaments, contain less paramyosin, and display structure that probably reflects the organization of the filament backbone which is not as apparent in images of Limulus filaments. We suggest that the similarities between Limulus and tarantula thick filaments may be governed, in part, by the close evolutionary relationship of the two species.

scholarly journals Myosin motors that cannot bind actin leave their folded OFF state on activation of skeletal muscle

2021 ◽  
Vol 153 (11) ◽  
Author(s):  
Massimo Reconditi ◽  
Elisabetta Brunello ◽  
Luca Fusi ◽  
Marco Linari ◽  
Vincenzo Lombardi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Binding Sites ◽  
Muscle Activation ◽  
Sarcomere Length ◽  
Rapid Change ◽  
Thick Filament ◽  
Actin Binding ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Myosin Motors

The myosin motors in resting skeletal muscle are folded back against their tails in the thick filament in a conformation that makes them unavailable for binding to actin. When muscles are activated, calcium binding to troponin leads to a rapid change in the structure of the actin-containing thin filaments that uncovers the myosin binding sites on actin. Almost as quickly, myosin motors leave the folded state and move away from the surface of the thick filament. To test whether motor unfolding is triggered by the availability of nearby actin binding sites, we measured changes in the x-ray reflections that report motor conformation when muscles are activated at longer sarcomere length, so that part of the thick filaments no longer overlaps with thin filaments. We found that the intensity of the M3 reflection from the axial repeat of the motors along the thick filaments declines almost linearly with increasing sarcomere length up to 2.8 µm, as expected if motors in the nonoverlap zone had left the folded state and become relatively disordered. In a recent article in JGP, Squire and Knupp challenged this interpretation of the data. We show here that their analysis is based on an incorrect assumption about how the interference subpeaks of the M3 reflection were reported in our previous paper. We extend previous models of mass distribution along the filaments to show that the sarcomere length dependence of the M3 reflection is consistent with <10% of no-overlap motors remaining in the folded conformation during active contraction, confirming our previous conclusion that unfolding of myosin motors on muscle activation is not due to the availability of local actin binding sites.

scholarly journals Bridgelike interconnections between thick filaments in stretched skeletal muscle fibers observed by the freeze-fracture method.

1986 ◽  
Vol 102 (3) ◽  
pp. 1093-1098 ◽  
Author(s):  
S Suzuki ◽  
G H Pollack
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Freeze Fracture ◽  
Thick Filament ◽  
Rapid Freezing ◽  
Semitendinosus Muscle ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Cross Bridges ◽  
Half Length

The ultrastructure of frog semitendinosus muscle was explored using the freeze-fracture, deep-etch, rotary-shadowing technique. Mechanically skinned fibers were stretched to decrease or eliminate the overlap of thick and thin filaments before rapid freezing with liquid propane. In relaxed, contracting, and rigor fibers, a significant number of bridgelike interconnections, distinct from those observed in the M-region, were observed between adjacent thick filaments in the non-overlap region. Their half-length and diameter corresponded approximately to the known dimensions of the cross-bridge (or myosin S-1). The interconnection may thus be formed by the binding of two apposed cross-bridges projecting from adjacent thick filaments. Fixation with 0.5% glutaraldehyde for 5-10 min before freezing effectively preserved these structures. The results indicate that the interconnections are genuine structures that appear commonly in stretched muscle fibers. They may play a role in stabilizing the thick filament lattice, and possibly in the contractile process.

scholarly journals Distinct contributions of the thin and thick filaments to length-dependent activation in heart muscle

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Xuemeng Zhang ◽  
Thomas Kampourakis ◽  
Ziqian Yan ◽  
Ivanka Sevrieva ◽  
Malcolm Irving ◽  
...  
Keyword(s):  
Heart Muscle ◽  
Structural Changes ◽  
Muscle Cells ◽  
Thick Filament ◽  
Calcium Sensitivity ◽  
Cellular Level ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Filament Structure ◽  
Heart Muscle Cells

The Frank-Starling relation is a fundamental auto-regulatory property of the heart that ensures the volume of blood ejected in each heartbeat is matched to the extent of venous filling. At the cellular level, heart muscle cells generate higher force when stretched, but despite intense efforts the underlying molecular mechanism remains unknown. We applied a fluorescence-based method, which reports structural changes separately in the thick and thin filaments of rat cardiac muscle, to elucidate that mechanism. The distinct structural changes of troponin C in the thin filaments and myosin regulatory light chain in the thick filaments allowed us to identify two aspects of the Frank-Starling relation. Our results show that the enhanced force observed when heart muscle cells are maximally activated by calcium is due to a change in thick filament structure, but the increase in calcium sensitivity at lower calcium levels is due to a change in thin filament structure.

scholarly journals Involvement of transglutaminase in myofibril assembly of chick embryonic myoblasts in culture.

1995 ◽  
Vol 130 (5) ◽  
pp. 1127-1136 ◽  
Author(s):  
S J Kang ◽  
K S Shin ◽  
W K Song ◽  
D B Ha ◽  
C H Chung ◽  
...  
Keyword(s):  
Competitive Inhibitor ◽  
Minimal Level ◽  
Thin Filaments ◽  
Thick Filaments ◽  
Tetradecanoyl Phorbol Acetate ◽  
Cross Striation ◽  
The Cross ◽  
Triton X ◽  
Developing Muscle

Involvement of transglutaminase in myofibrillogenesis of chick embryonic myoblasts has been investigated in vitro. Both the activity and protein level of transglutaminase initially decreased to a minimal level at the time of burst of myoblast fusion but gradually increased thereafter. The localization of transglutaminase underwent a dramatic change from the whole cytoplasm in a diffuse pattern to the cross-striated sarcomeric A band, being strictly colocalized with the myosin thick filaments. For a brief period prior to the appearance of cross-striation, transglutaminase was localized in nonstriated filamental structures that coincided with the stress fiber-like structures. When 12-o-tetradecanoyl phorbol acetate was added to muscle cell cultures to induce the sequential disassembly of thin and thick filaments, transglutaminase was strictly colocalized with the myosin thick filaments even in the myosacs, of which most of the thin filaments were disrupted. Moreover, monodansylcadaverine, a competitive inhibitor of transglutaminase, reversibly inhibited the myofibril maturation. In addition, myosin heavy chain behaved as one of the potential intracellular substrates for transglutaminase. The cross-linked myosin complex constituted approximately 5% of the total Triton X-100-insoluble pool of myosin molecules in developing muscle cells, and its level was reduced to below 1% upon treatment with monodansylcadaverine. These results suggest that transglutaminase plays a crucial role in myofibrillogenesis of developing chick skeletal muscle.

scholarly journals THE FINE STRUCTURE OF THE VENTRAL INTERSEGMENTAL ABDOMINAL MUSCLES OF THE INSECT RHODNIUS PROLIXUS DURING THE MOLTING CYCLE

1968 ◽  
Vol 37 (2) ◽  
pp. 445-461 ◽  
Author(s):  
Paul A. Toselli ◽  
Frank A. Pepe
Keyword(s):  
Fine Structure ◽  
Insect Flight ◽  
Motor Nerve ◽  
Thick Filament ◽  
Rhodnius Prolixus ◽  
Abdominal Muscles ◽  
Molting Cycle ◽  
Thin Filaments ◽  
Characteristic Structure ◽  
Thick Filaments

Rhodnius prolixus, a South American insect, molts five times in its development to an adult after emerging from the egg. Each molting cycle is triggered with a blood-meal. The ventral intersegmental abdominal muscles of Rhodnius develop during each molting cycle and are functional at molting. The fine structure of these fully developed muscles from fourth stage larval insects is studied. They have the characteristic structure of slow muscles. They have multiple motor nerve endings, and the myofibrils are poorly defined in cross-section. Longitudinal sections show long sarcomeres (8–10 µ), irregular Z-lines, and no apparent H zones. No M line is seen. Transverse sections through the A-band region show that each hexagonally arranged thick filament is surrounded by 12 thin filaments. Two thin filaments are shared by two neighboring thick filaments. The ratio of thin to thick filaments is 6:1. This structure is related to that found in vertebrate skeletal muscle and insect flight muscle.

scholarly journals CARDIAC MUSCLE OF THE HORSESHOE CRAB, LIMULUS POLYPHEMUS

1971 ◽  
Vol 48 (1) ◽  
pp. 101-119 ◽  
Author(s):  
R. A. Leyton ◽  
E. H. Sonnenblick
Keyword(s):  
Cardiac Muscle ◽  
Horseshoe Crab ◽  
Thick Filament ◽  
Limulus Polyphemus ◽  
Cell Junctions ◽  
Thin Filaments ◽  
Intercalated Discs ◽  
Thick Filaments ◽  
Structural Details ◽  
Intercellular Clefts

The fine structure of the cardiac muscle of the horseshoe crab, Limulus polyphemus, has been studied with respect to the organization of its contractile material, and the structure of its organelles and the cell junctions. Longitudinal sections show long sarcomeres (5.37 µ at Lmax), wide A bands (2.7 µ), irregular Z lines, no M line, and no apparent H zone. Transverse sections through the S zone of the A band show that each thick filament is ca. 180 A in diameter, is circular in profile with a center of low density, and is surrounded by an orbit of 9–12 thin filaments, each 60 A in diameter. Thick filaments are confined to the A band: thin filaments originate at the Z band, extend through the I band, and pass into the A band between the thick filaments. The sarcolemmal surface area is increased significantly by intercellular clefts. Extending into the fiber from these clefts and from the sarcolemma, T tubules pass into the fiber at the A-I level. Each fibril is enveloped by a profuse membranous covering of sarcoplasmic reticulum (SR). Sacculations of the SR occur at the A-I boundary where they make diadic contact with longitudinal branches of the T system. These branches also extend toward the Z, enlarge at the Z line, and pass into the next sarcomere. Infrequently noted were intercalated discs possessing terminal insertion and desmosome modifications, but lacking close junctions (fasciae occludentes). These structural details are compared with those of mammalian cardiac and invertebrate muscles.

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