scholarly journals ELECTROMECHANICAL COUPLING IN TUBULAR MUSCLE FIBERS

1972 ◽  
Vol 52 (3) ◽  
pp. 626-638 ◽  
Author(s):  
Arieh Gilai ◽  
I. Parnas
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cell Membrane ◽  
Electromechanical Coupling ◽  
Surface Membrane ◽  
Hexagonal Array ◽  
Thin Filaments ◽  
Transverse Tubular System ◽  
The Core ◽  
Tubular System ◽  
Terminal Cisternae

The tubular fibers of the claw-closer muscle of the scorpion have a central core containing nuclei and mitochondria. The myofibrils have the shape of thin lamellae (1 µ) extending radially from the core to the surface membrane (20 µ). The thick myofilaments are organized in a hexagonal array with orbits of 10–13 thin myofilaments. The ratio of thick-to-thin filaments is 1:5. Transverse tubular system (TS) openings are located between lamellated myofibrils. In each sarcomere two TS's are found, one on each side of the H band. The TS is composed of a transverse tubule and tubular pockets (TP). The TP's form diadic contact with the terminal cisternae of the sarcoplasmic reticulum. The TS can be traced from the cell membrane down to the cell core. The surface area of the TS was calculated to be six times that of the outer surface membrane.

Sarcoplasmic reticulum and mitochondria as cation accumulation sites in smooth muscle

1973 ◽  
Vol 265 (867) ◽  
pp. 17-23 ◽  
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Divalent Cation ◽  
Electromechanical Coupling ◽  
Surface Membrane ◽  
Smooth Muscles ◽  
Relative Volume ◽  
Electron Dense Material ◽  
Tubular System ◽  
Central Elements

A tubular system of sarcoplasmic reticulum that is not penetrated by extracellular markers is described in vertebrate smooth muscles. The sarcoplasmic reticulum forms fenestrations around the surface vesicles and also forms close appositions (an approximately 10 to 12 nm gap traversed by periodic electron dense material) with the non-specialized surface membrane. The morphological couplings are considered to be the most probable sites of electromechanical coupling of the action potential to the twitch contraction. The relative volume of the sarcoplasmic reticulum varies in functionally different (tonic and phasic) smooth muscles, and correlates with the ability of the different smooth muscles to contract in the absence of extracellular calcium. Electron opaque deposits of strontium are accumulated by peripheral and central elements of the sarcoplasmic reticulum. The accumulation of strontium and barium by mitochondria raises the possibility that, in addition to the sarcoplasmic reticulum, mitochondria may play a role in the regulation of intracellular divalent cation levels in vertebrate smooth muscle.

scholarly journals THE SARCOPLASMIC RETICULUM AND ITS ASSOCIATION WITH THE T SYSTEM IN AN INSECT

1967 ◽  
Vol 32 (3) ◽  
pp. 535-545 ◽  
Author(s):  
Martin Hagopian ◽  
David Spiro
Keyword(s):  
Fine Structure ◽  
Sarcoplasmic Reticulum ◽  
Cell Surface ◽  
Osmium Tetroxide ◽  
Surface Membrane ◽  
Transverse Tubular System ◽  
Leucophaea Maderae ◽  
Tubular System ◽  
Femoral Muscle ◽  
T System

The fine structure of the sarcoplasmic reticulum and the transverse tubular system of the femoral muscle of the cockroach, Leucophaea maderae, was studied after prefixation in glutaraldehyde, postfixation in osmium tetroxide, and embedding in Epon. The sarcoplasmic reticulum in this muscle reveals features not previously reported. The sarcoplasmic reticulum is abundant, consisting mainly of a fenestrated envelope which surrounds each myofibril at all levels in the sarcomere. This sarcoplasmic reticulum envelope is continuous transversally as well as longitudinally along the myofibrils. Dyadic junctions are formed by a single T system element which contacts the unfenestrated sarcoplasmic reticulum of adjacent myofibrils in an alternating manner at the ends of the A band. At the dyads, regularly spaced thickenings of the sarcoplasmic reticulum membranes bordering the dyadic spaces are noted. These thickenings, however, do not contact the T tubule membrane. Typical dyadic contacts also are seen between the cell surface membrane and sarcoplasmic reticulum. Z line-like material is seen in contact with the membranes of the cell surface and longitudinal branches of the T systems.

scholarly journals THE STRUCTURE OF INTERSEGMENTAL MUSCLE FIBERS IN AN INSECT, PERIPLANETA AMERICANA L

1966 ◽  
Vol 29 (3) ◽  
pp. 449-459 ◽  
Author(s):  
David S. Smith
Keyword(s):  
Periplaneta Americana ◽  
Flight Muscle ◽  
Muscle Fibers ◽  
Structural Features ◽  
Mitochondrial Content ◽  
Thin Filaments ◽  
Transverse Tubular System ◽  
Thick Filaments ◽  
Tubular System ◽  
Contraction And Relaxation

The organization of intersegmental muscle fibers associated with the dorsal abdominal sclerites of the cockroach is described. These fibers correspond closely, in the disposition and derivation of the membranes of the transverse tubular system and sarcoplasmic reticulum cisternae, with insect synchronous flight muscle fibers, but differ markedly from these in their fibrillar architecture and mitochondrial content. The mitochondria are small and generally aligned alongside the prominent I bands of the sarcomere, and, in the best-oriented profiles of the A bands, thick filaments are associated with orbitals of twelve thin filaments, a configuration that has also been observed in striated fibers of insect visceral muscle. These structural features of insect muscles are compared and discussed in terms of possible variations in the control of contraction and relaxation, and in the nature of their mechanical role.

scholarly journals SARCOPLASMIC RETICULUM AND EXCITATION-CONTRACTION COUPLING IN MAMMALIAN SMOOTH MUSCLES

1972 ◽  
Vol 52 (3) ◽  
pp. 690-718 ◽  
Author(s):  
Carrick E. Devine ◽  
Avril V. Somlyo ◽  
Andrew P. Somlyo
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Pulmonary Artery ◽  
Mesenteric Artery ◽  
Electromechanical Coupling ◽  
Surface Membrane ◽  
Main Pulmonary Artery ◽  
Smooth Muscles ◽  
Taenia Coli ◽  
Virtual Absence ◽  
Mesenteric Vein

The sarcoplasmic reticulum (SR) was studied in the smooth muscles of rabbit main pulmonary artery, mesenteric vein, aorta, mesenteric artery, taenia coli, guinea pig mesenteric artery, and human uterus, and correlated with contractions of the smooth muscles in Ca-free media. SR volumes were determined in main pulmonary artery (5.1%), aorta (5%), portal-anterior mesenteric vein (2.2%), taenia coli (2%), and mesenteric artery (1.8%): because of tangentially sectioned membranes these estimates are subject to a correction factor of up to +50% of the values measured. Smooth muscles that contained a relatively large volume of SR maintained significant contractile responses to drugs in the virtual absence of extracellular calcium at room temperatures, while smooth muscles that had less SR did not. The unequal maximal contractions of main pulmonary artery elicited by different drugs were also observed in Ca-free, high potassium-depolarizing solution, indicating that they were secondary to some mechanism independent of changes in membrane potential or calcium influx. Longitudinal tubules of SR run between and are fenestrated about groups of surface vesicles separated from each other by intervening dense bodies. Extracellular markers (ferritin and lanthanum) entered the surface vesicles, but not the SR. The peripheral SR formed couplings with the surface membrane: the two membranes were separated by gaps of approximately 10 nm traversed by electron-opaque connections suggestive of a periodicity of approximately 20–25 nm. These couplings are considered to be the probable sites of electromechanical coupling in twitch smooth muscles. Close contacts between the SR and the surface vesicles may have a similar function, or represent sites of calcium extrusion. The presence of both thick and thin myofilaments and of rough SR in smooth muscles supports the dual, contractile and morphogenetic, function of smooth muscle.

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.

scholarly journals THE FINE STRUCTURE OF FAST AND SLOW CRUSTACEAN MUSCLES

1967 ◽  
Vol 35 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Wolf H. Fahrenbach
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Sarcomere Length ◽  
Morphological Type ◽  
Slow Muscle ◽  
Anatomical Location ◽  
Hexagonal Array ◽  
Cancer Magister ◽  
Thin Filaments ◽  
Cypridopsis Vidua ◽  
Postural Muscles

Known phasic and tonic muscle fibers of the crab Cancer magister were studied by electron microscopy. Phasic fibers have sarcomeres about 4.5 µ long, small polygonal myofibrils, and a well-developed sarcoplasmic reticulum. The thick myofilaments, disposed in hexagonal array, are each surrounded by six thin filaments. The tonic fibers have a sarcomere length of about 12 µ, larger myofibrils, a poorly developed sarcoplasmic reticulum, and a disorderly array of myofilaments. Each thick myofilament is surrounded by 10–12 thin filaments. The same morphological type of slow muscle has been found in the crustaceans, Macrocyclops albidus, Cypridopsis vidua, and Balanus cariosus, in each case in an anatomical location consistent with tonic action. A search of the literature indicates that this type of muscle is found in all classes of arthropods and is confined to visceral and postural muscles or specializations of these.

scholarly journals Coordinated Incorporation of Skeletal Muscle Dihydropyridine Receptors and Ryanodine Receptors in Peripheral Couplings of BC3H1 Cells

1997 ◽  
Vol 137 (4) ◽  
pp. 859-870 ◽  
Author(s):  
Feliciano Protasi ◽  
Clara Franzini-Armstrong ◽  
Bernhard E. Flucher
Keyword(s):  
Skeletal Muscle ◽  
Calcium Release ◽  
Surface Membrane ◽  
Ryanodine Receptors ◽  
Freeze Fracture ◽  
Cell Periphery ◽  
Calcium Release Channels ◽  
Transverse Tubular System ◽  
Dihydropyridine Receptors ◽  
Tubular System

Rapid release of calcium from the sarcoplasmic reticulum (SR) of skeletal muscle fibers during excitation–contraction (e–c) coupling is initiated by the interaction of surface membrane calcium channels (dihydropyridine receptors; DHPRs) with the calcium release channels of the SR (ryanodine receptors; RyRs, or feet). We studied the early differentiation of calcium release units, which mediate this interaction, in BC3H1 cells. Immunofluorescence labelings of differentiating myocytes with antibodies against α1 and α2 subunits of DHPRs, RyRs, and triadin show that the skeletal isoforms of all four proteins are abundantly expressed upon differentiation, they appear concomitantly, and they are colocalized. The transverse tubular system is poorly organized, and thus clusters of e–c coupling proteins are predominantly located at the cell periphery. Freeze fracture analysis of the surface membrane reveals tetrads of large intramembrane particles, arranged in orderly arrays. These appear concomitantly with arrays of feet (RyRs) and with the appearance of DHPR/RyS clusters, confirming that the four components of the tetrads correspond to skeletal muscle DHPRs. The arrangement of tetrads and feet in developing junctions indicates that incorporation of DHPRs in junctional domains of the surface membrane proceeds gradually and is highly coordinated with the formation of RyR arrays. Within the arrays, tetrads are positioned at a spacing of twice the distance between the feet. The incorporation of individual DHPRs into tetrads occurs exclusively at positions corresponding to alternate feet, suggesting that the assembly of RyR arrays not only guides the assembly of tetrads but also determines their characteristic spacing in the junction.

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