scholarly journals STRUCTURE OF THE LONGITUDINAL BODY MUSCLES OF AMPHIOXUS

1961 ◽  
Vol 10 (4) ◽  
pp. 159-176 ◽  
Author(s):  
Lee D. Peachey
Keyword(s):  
Electron Microscopy ◽  
Plasma Membrane ◽  
Sarcoplasmic Reticulum ◽  
Internal Structure ◽  
Striated Muscle ◽  
Light And Electron Microscopy ◽  
Maximum Distance ◽  
Hexagonal Array ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling

The structure of the longitudinal body muscles of Branchiostoma caribaeum has been studied by light and electron microscopy. These muscles are shown to be composed of fibers in the form of flat lamellae about 0.8µ in thickness, more than 100 µ wide, and reaching in length from one intermuscular septum to the next, a distance of about 0.6 mm. Each flat fiber is covered by a plasma membrane and contains a single myofibril consisting of myofilaments packed in the interdigitating hexagonal array characteristic of vertebrate striated muscle. Little or no sarcoplasmic reticulum is present. Mitochondria are found infrequently and have a tubular internal structure. These morphological observations are discussed in relation to a proposed hypothesis of excitation-contraction coupling. It is pointed out that the maximum distance from surface to myofilament in these muscles is about 0.5 µ and that diffusion of an "activating" substance over this distance would essentially be complete in less than 0.5 msec. after its release from the plasma membrane. It is concluded that the flat form of amphioxus muscle substitutes for the specialized mechanisms of excitation-contraction coupling thought possibly to involve the sarcoplasmic reticulum in higher vertebrate muscles.

scholarly journals CARDIAC MUSCLE

1968 ◽  
Vol 36 (3) ◽  
pp. 497-526 ◽  
Author(s):  
Joachim R. Sommer ◽  
Edward A. Johnson
Keyword(s):  
Electron Microscopy ◽  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Cardiac Muscle ◽  
Extracellular Space ◽  
Light And Electron Microscopy ◽  
Rabbit Heart ◽  
Contraction Coupling ◽  
The Difference

With light and electron microscopy a comparison has been made of the morphology of ventricular (V) and Purkinje (P) fibers of the hearts of guinea pig, rabbit, cat, dog, goat, and sheep. The criteria, previously established for the rabbit heart, that V fibers are distinguished from P fibers by the respective presence and absence of transverse tubules is shown to be true for all animals studied. No evidence was found of a permanent connection between the sarcoplasmic reticulum and the extracellular space. The sarcoplasmic reticulum (SR) of V fibers formed couplings with the sarcolemma of a transverse tubule (interior coupling) and with the peripheral sarcolemma (peripheral coupling), whereas in P fibers the SR formed only peripheral couplings. The forms of the couplings were identical. The significance, with respect to excitation-contraction coupling, of the difference in the form of the couplings in cardiac versus skeletal muscle is discussed together with the electrophysiological implications of the differing geometries of bundles of P fibers from different animals.

Ryanodine receptors of striated muscles: a complex channel capable of multiple interactions

1997 ◽  
Vol 77 (3) ◽  
pp. 699-729 ◽  
Author(s):  
C. Franzini-Armstrong ◽  
F. Protasi
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Striated Muscle ◽  
Surface Membrane ◽  
Ryanodine Receptors ◽  
Striated Muscles ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Dihydropyridine Receptors ◽  
Long Range Interactions ◽  
Cardiac Muscles

The ryanodine receptor (RyR) is a high-conductance Ca2+ channel of the sarcoplasmic reticulum in muscle and of the endoplasmic reticulum in other cells. In striated muscle fibers, RyRs are responsible for the rapid release of Ca2+ that activates contraction. Ryanodine receptors are complex molecules, with unusually large cytoplasmic domains containing numerous binding sites for agents that control the state of activity of the channel-forming domain of the molecule. Structural considerations indicate that long-range interactions between cytoplasmic and intramembrane domains control channel function. Ryanodine receptors are located in specialized regions of the SR, where they are structurally and functionally associated with other intrinsic proteins and, indirectly, also with the luminal Ca2(+)-binding protein calsequestrin. Activation of RyRs during the early part of the excitation-contraction coupling cascade is initiated by the activity of surface-membrane Ca2+ channels, the dihydropyridine receptors (DHPRs). Skeletal and cardiac muscles contain different RyR and DHPR isoforms and both contribute to the diversity in cardiac and skeletal excitation-contraction coupling mechanisms. The architecture of the sarcoplasmic reticulum-surface junctions determines the types of RyR-DHPR interactions in the two muscle types.

scholarly journals Triadin Binding to the C-Terminal Luminal Loop of the Ryanodine Receptor is Important for Skeletal Muscle Excitation–Contraction Coupling

2007 ◽  
Vol 130 (4) ◽  
pp. 365-378 ◽  
Author(s):  
Sanjeewa A. Goonasekera ◽  
Nicole A. Beard ◽  
Linda Groom ◽  
Takashi Kimura ◽  
Alla D. Lyfenko ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Ryanodine Receptor ◽  
Calcium Release ◽  
Striated Muscle ◽  
Single Channel ◽  
Triple Mutant ◽  
Double Mutation ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling ◽  
Functional Studies

Ca2+ release from intracellular stores is controlled by complex interactions between multiple proteins. Triadin is a transmembrane glycoprotein of the junctional sarcoplasmic reticulum of striated muscle that interacts with both calsequestrin and the type 1 ryanodine receptor (RyR1) to communicate changes in luminal Ca2+ to the release machinery. However, the potential impact of the triadin association with RyR1 in skeletal muscle excitation–contraction coupling remains elusive. Here we show that triadin binding to RyR1 is critically important for rapid Ca2+ release during excitation–contraction coupling. To assess the functional impact of the triadin-RyR1 interaction, we expressed RyR1 mutants in which one or more of three negatively charged residues (D4878, D4907, and E4908) in the terminal RyR1 intraluminal loop were mutated to alanines in RyR1-null (dyspedic) myotubes. Coimmunoprecipitation revealed that triadin, but not junctin, binding to RyR1 was abolished in the triple (D4878A/D4907A/E4908A) mutant and one of the double (D4907A/E4908A) mutants, partially reduced in the D4878A/D4907A double mutant, but not affected by either individual (D4878A, D4907A, E4908A) mutations or the D4878A/E4908A double mutation. Functional studies revealed that the rate of voltage- and ligand-gated SR Ca2+ release were reduced in proportion to the degree of interruption in triadin binding. Ryanodine binding, single channel recording, and calcium release experiments conducted on WT and triple mutant channels in the absence of triadin demonstrated that the luminal loop mutations do not directly alter RyR1 function. These findings demonstrate that junctin and triadin bind to different sites on RyR1 and that triadin plays an important role in ensuring rapid Ca2+ release during excitation–contraction coupling in skeletal muscle.

Formation of chlamydospores in Gilbertella persicaria

1981 ◽  
Vol 59 (5) ◽  
pp. 908-928 ◽  
Author(s):  
Martha J. Powell ◽  
Charles E. Bracker ◽  
David J. Sternshein
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Acid Phosphatase ◽  
Light And Electron Microscopy ◽  
Multivesicular Bodies ◽  
Marker Enzyme ◽  
Transparent Layer ◽  
Thiamine Pyrophosphatase ◽  
Gilbertella Persicaria

The cytological events involved in the transformation of vegetative hyphae of the zygomycete Gilbertella persicaria (Eddy) Hesseltine into chlamydospores were studied with light and electron microscopy. Thirty hours after sporangiospores were inoculated into YPG broth, swellings appeared along the aseptate hyphae. Later, septa, traversed by plasmodesmata, delimited each end of the hyphal swellings and compartmentalized these hyphal regions as they differentiated into chlamydospores. Nonswollen regions adjacent to chlamydospores remained as isthmuses. Two additional wall layers appeared within the vegetative wall of the developing chlamydospores. An alveolate, electron-dense wall formed first, and then an electron-transparent layer containing concentrically oriented fibers formed between this layer and the plasma membrane. Rather than a mere condensation of cytoplasm, development and maturation of the multinucleate chlamydospores involved extensive cytoplasmic changes such as an increase in reserve products, lipid and glycogen, an increase and then disappearance of vacuoles, and the breakdown of many mitochondria. Underlying the plasma membrane during chlamydospore wall formation were endoplasmic reticulum, multivesicular bodies, vesicles with fibrillar contents, vesicles with electron-transparent contents, and cisternal rings containing the Golgi apparatus marker enzyme, thiamine pyrophosphatase. Acid phosphatase activity was localized cytochemically in a cisterna which enclosed mitochondria and in vacuoles which contained membrane fragments. Tightly packed membrane whorls and single membrane bounded sacs with finely granular matrices surrounding vacuoles were unique during chlamydospore development. Microbodies were rare in the mature chlamydospore, but endoplasmic reticulum was closely associated with lipid globules. As chlamydospores developed, the cytoplasm in the isthmus became highly vacuolated, lipid globules were closely associated with vacuoles, mitochondria were broken down in vacuoles, unusual membrane configurations appeared, and eventually the membranes degenerated. Unlike chlamydospores, walls of the isthmus did not thicken, but irregularly shaped appositions containing numerous channels formed at intervals on the inside of these walls. The pattern of cytoplasmic transformations during chlamydospore development is similar to events leading to the formation of zygospores and sporangiospores.

scholarly journals Immunofluorescence and electron microscopy of the cytoplasmic surface of the human erythrocyte membrane and its interaction with Sendai virus.

1979 ◽  
Vol 83 (2) ◽  
pp. 338-347 ◽  
Author(s):  
M Büechi ◽  
T Bächi
Keyword(s):  
Electron Microscopy ◽  
Plasma Membrane ◽  
Plasma Membranes ◽  
Sendai Virus ◽  
Light And Electron Microscopy ◽  
Distal Portion ◽  
Double Labeling ◽  
Virus Particles ◽  
Viral Antigens ◽  
Cytoplasmic Surface

A method was developed for directly observing the inner surfaces of plasma membranes by light and electron microscopy. Human erythrocytes were attached to cover slips (glass or mica) treated with aminopropylsilane and glutaraldehyde, and then disrupted by direct application of a jet of buffer, which removed the distal portion of the cells, thus exposing the cytoplasmic surface (PS) of the flattened membranes. Antispectrin antibodies and Sendai virus particles were employed as sensitive markers for, respectively, the PS and the external surface (ES) of the membrane; their localization by immunofluorescence or electron microscopy demonstrated that the major asymmetrical features of the plasma membrane were preserved. The fusion of Sendai virus particles with cells was investigated using double-labeling immunofluorescence techniques. Virus adsorbed to the ES of cells at 4 degrees C was not accessible to fluorescein-labeled antibodies applied from the PS side. After incubation at 37 degrees C, viral antigens could be detected at the PS. These antigens, however, remained localized and did not diffuse from the site of attachment, as is usually seen in viral antigens accessible on the ES. They may therefore represent internal viral antigens not incorporated into the plasma membrane as a result of virus-cell fusion.

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