The Anatomy of the Sarcoplasmic Reticulum in Vertebrate Skeletal Muscle: Its Implications for Excitation Contraction Coupling

1982 ◽  
Vol 37 (7-8) ◽  
pp. 665-678 ◽  
Author(s):  
Joachim R. Sommer
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Action Potential ◽  
Cardiac Muscle ◽  
Calcium Release ◽  
Striated Muscle ◽  
Band Region ◽  
Terminal Cisterna ◽  
Transmitter Substance ◽  
Main Components

Abstract The sarcoplasmic reticulum in situ is an intricate tubular network that surrounds the contractile material in striated muscle cells. Its topographical relationship to other intracellular components, especially the myofibrils, is rather rigidly mainiained by a cytoskeleton which enmeshes Z line material and sarcoplasmic reticulum and, ultimately, is anchored at the plasmalemma. As a result, the two main components of the sarcoplasmic reticulum, the junctional SR and the free SR, retain their typical location in the A band region and in the I band region, respectively. The junc­tional SR, which is thought to be the site for calcium storage and release for contraction, is, thus, always well within one micron of the regulatory proteins associated with the actin filaments. The junctional SR, a synonym for terminal cisterna applying to both skeletal and cardiac muscle, is generally held to be involved in the translation of the action potential into calcium release, mainly because of the close topographic apposition between the junctional SR and the plasmalemma, especially in skeletal muscle. This attractive structure-function correlation is challenged by the observation that in bird cardiac muscle 80% of the junctional SR is spacially far removed from plas­malemma, the site of electrical activity. This anomalous topography is not in conflict with the notion that translation of the action potential into calcium release may be accomplished by a dif­fusible transmitter substance, e.g. calcium. Any hypothesis dealing with this problem must ac­ count for the anatomy of the bird heart.

scholarly journals The Builders of the Junction: Roles of Junctophilin1 and Junctophilin2 in the Assembly of the Sarcoplasmic Reticulum–Plasma Membrane Junctions in Striated Muscle

Biomolecules ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 109
Author(s):  
Stefano Perni
Keyword(s):  
Plasma Membrane ◽  
Sarcoplasmic Reticulum ◽  
Intracellular Calcium ◽  
Cardiac Muscle ◽  
Structure Prediction ◽  
Calcium Release ◽  
Striated Muscle ◽  
Short Review ◽  
Published Data ◽  
Intracellular Calcium Release

Contraction of striated muscle is triggered by a massive release of calcium from the sarcoplasmic reticulum (SR) into the cytoplasm. This intracellular calcium release is initiated by membrane depolarization, which is sensed by voltage-gated calcium channels CaV1.1 (in skeletal muscle) and CaV1.2 (in cardiac muscle) in the plasma membrane (PM), which in turn activate the calcium-releasing channel ryanodine receptor (RyR) embedded in the SR membrane. This cross-communication between channels in the PM and in the SR happens at specialized regions, the SR-PM junctions, where these two compartments come in close proximity. Junctophilin1 and Junctophilin2 are responsible for the formation and stabilization of SR-PM junctions in striated muscle and actively participate in the recruitment of the two essential players in intracellular calcium release, CaV and RyR. This short review focuses on the roles of junctophilins1 and 2 in the formation and organization of SR-PM junctions in skeletal and cardiac muscle and on the functional consequences of the absence or malfunction of these proteins in striated muscle in light of recently published data and recent advancements in protein structure prediction.

Impaired calcium release during fatigue

2008 ◽  
Vol 104 (1) ◽  
pp. 296-305 ◽  
Author(s):  
D. G. Allen ◽  
G. D. Lamb ◽  
H. Westerblad
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Action Potential ◽  
Inorganic Phosphate ◽  
Calcium Release ◽  
Voltage Sensor ◽  
Functional Importance ◽  
Intracellular Atp ◽  
Channel Opening ◽  
Sensor Activation

Impaired calcium release from the sarcoplasmic reticulum (SR) has been identified as a contributor to fatigue in isolated skeletal muscle fibers. The functional importance of this phenomenon can be quantified by the use of agents, such as caffeine, which can increase SR Ca2+ release during fatigue. A number of possible mechanisms for impaired calcium release have been proposed. These include reduction in the amplitude of the action potential, potentially caused by extracellular K+ accumulation, which may reduce voltage sensor activation but is counteracted by a number of mechanisms in intact animals. Reduced effectiveness of SR Ca2+ channel opening is caused by the fall in intracellular ATP and the rise in Mg2+ concentrations that occur during fatigue. Reduced Ca2+ available for release within the SR can occur if inorganic phosphate enters the SR and precipitates with Ca2+. Further progress requires the development of methods that can identify impaired SR Ca2+ release in intact, blood-perfused muscles and that can distinguish between the various mechanisms proposed.

Filipin-Sterol-Complexes in Finch and Mouse Cardiac Muscle

1981 ◽  
Vol 39 ◽  
pp. 504-505
Author(s):  
J. R. Sommer
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Plasma Membranes ◽  
Frog Skeletal Muscle ◽  
Transverse Tubules ◽  
Topographic Features ◽  
Terminal Cisterna ◽  
Close Proximity

We have recently reported that in frog skeletal muscle the plasma membranes, including the transverse tubules, are densely populated by filipin-sterol-complexes (FC), and that in the sarcoplasmic reticulum (SR) the FC are found much less commonly than in the plasma membrane, but that they have a predilection for the junctional SR (terminal cisterna) which in skeletal muscle are very large cisternae that are in close proximity to the plasma membrane. The analogous junctional SR of cardiac muscle shares all anatomical and topographic features with the junctional SR of skeletal muscle, except that in the latter the junctional SR is much larger. Ue have considered the possibility that the proximity of the junctional SR to the plasma membrane, the latter being replete with FC, may be related to the predilection of the FC for junctional SR in skeletal muscle.

Corbular (CSR) and extended junctional SR (EJSR) in skeletal muscle

1994 ◽  
Vol 52 ◽  
pp. 192-193
Author(s):  
J. R. Sommer ◽  
T. D. High ◽  
I. Taylor
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Muscle ◽  
Calcium Release ◽  
Striated Muscle ◽  
Volume Fraction ◽  
Signal Transmission ◽  
Calcium Stores ◽  
Physical Interaction ◽  
One Step ◽  
Calcium Induced Calcium Release

Excitation-calcium release (ECR) is one of the first steps in excitation-contraction coupling in striated muscle. In skeletal muscle, there is some evidence that ECR depends on physical interaction between electrical activity at the plasmalemma (PL) and intracellular calcium stores (junctional sarcoplasmic reticulum; JSR). In cardiac muscle, there is very strong evidence for signal transmission from PL through the release of a diffusible transmitter substance, initially at couplings (= JSR tightly apposed to PL). Avian cardiac muscle has no transverse tubules (TT) but JSR, both as part of peripheral couplings (25%) and as extended JSR (EJSR) unattached to PL (75%). A subset of EJSR, corbular SR (CSR), occurs in small numbers in mammalian hearts and, topographically, fills in wherever TT and, thus, interior couplings (i.e. JSR) are missing. The total volume fraction of avian EJSR (75%) + JSR (25%) is identical to murine JSR (>90%) + CSR (< 10%). JSR-total (JSR, EJSR, CSR) establishes calcium release sites at about equidistant locations throughout the volume of a myocyte. Whereas, in avian hearts a signal for calcium release initiated at a peripheral coupling must be propagated transversely for up to 4 μm (cell radius) by quasi “saltatory” propagation of calcium-induced calcium release (CICR) along the EJSR’s junctional processes (JPs = ryanodine sites) eliciting calcium release for contraction at each contact, in mammalian cardiac and in skeletal muscle calcium release is effected in a one-step process through a propagated action potential kickstarting calcium release at each of a string of peripheral and interior couplings located along TT.

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.

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