scholarly journals Extended junctional sarcoplasmic reticulum of avian cardiac muscle contains functional ryanodine receptors.

1994 ◽  
Vol 269 (3) ◽  
pp. 1627-1634
Author(s):  
J. Junker ◽  
J.R. Sommer ◽  
M. Sar ◽  
G. Meissner
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptors ◽  
Junctional Sarcoplasmic Reticulum

Anchorfibers and the Topography of Junctional SR

1977 ◽  
Vol 35 ◽  
pp. 582-583
Author(s):  
James Junker ◽  
Joachim R. Sommer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Single Filament ◽  
Relaxation Cycle ◽  
10 Nm Filaments ◽  
Junctional Sarcoplasmic Reticulum

Junctional sarcoplasmic reticulum (JSR) in all its forms (extended JSR, JSR of couplings, corbular SR) in both skeletal and cardiac muscle is always located at the Z - I regions of the sarcomeres. The Z tubule is a tubule of the free SR (non-specialized SR) which is consistently located at the Z lines in cardiac muscle (1). Short connections between JSR and Z lines have been described (2), and bundles of filaments at Z lines have been seen in skeletal (3) and cardiac (4) muscle. In opossum cardiac muscle, we have seen bundles of 10 nm filaments stretching across interfibrillary spaces and adjacent myofibrils with extensions to the plasma- lemma in longitudinal (Fig. 1) and transverse (Fig. 2) sections. Only an occasional single filament is seen elsewhere along a sarcomere. We propose that these filaments represent anchor fibers that maintain the observed invariant topography of the free SR and JSR throughout the contraction-relaxation cycle.

Calcium is released from the junctional sarcoplasmic reticulum during cardiac muscle contraction

1991 ◽  
Vol 260 (3) ◽  
pp. H989-H997 ◽  
Author(s):  
C. S. Moravec ◽  
M. Bond
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Muscle Contraction ◽  
Cardiac Muscle ◽  
Electron Probe Microanalysis ◽  
Electron Probe ◽  
Storage Site ◽  
Papillary Muscles ◽  
Cardiac Muscle Contraction ◽  
Intracellular Storage ◽  
Junctional Sarcoplasmic Reticulum

We have used electron-probe microanalysis (EPMA) to address the question of Ca2+ release by junctional sarcoplasmic reticulum (JSR) as well as Ca2+ regulation by mitochondria (MT) during cardiac muscle contraction. Hamster papillary muscles were rapidly frozen during relaxation or at the peak rate of tension rise (+dT/dt). Total Ca2+ content was measured by EPMA in the JSR, within a MT, over the A band, and in the whole cell, in nine cells per animal (five animals per group). JSR Ca2+ content was found to be significantly lower in muscles frozen at the peak of contraction [7.3 +/- 1.3 (mean +/- SE) mmol Ca2+/kg dry wt] than in those frozen during relaxation (12.5 +/- 1.9 mmol Ca2+/kg dry wt; P less than 0.01), suggesting that Ca2+ is released from this storage site during cardiac muscle contraction. In contrast, MT Ca2+ content did not change significantly during contraction (0.4 +/- 0.1 mmol/kg dry wt) compared with relaxation (0.1 +/- 0.2 mmol/kg dry wt). A third group of muscles was frozen during relaxation after pretreatment with 10(-7) M ryanodine. Ca2+ content of the JSR was significantly decreased (P less than 0.01) in this group of muscles, (6.4 +/- 1.8 mmol/kg dry wt) compared with those frozen during relaxation in the absence of the drug. This suggests that the intracellular storage site with a decreased Ca2+ content in muscles frozen at the peak of contraction is the ryanodine-releasable store. These results provide the first direct measurement of the Ca2+ content of both JSR and MT during a normal cardiac muscle contraction and demonstrate that Ca2+ is released from the JSR during muscle contraction.

scholarly journals Interaction of the Joining Region in Junctophilin-2 With the L-Type Ca 2+ Channel Is Pivotal for Cardiac Dyad Assembly and Intracellular Ca 2+ Dynamics

2021 ◽  
Vol 128 (1) ◽  
pp. 92-114
Author(s):  
Polina Gross ◽  
Jaslyn Johnson ◽  
Carlos M. Romero ◽  
Deborah M. Eaton ◽  
Claire Poulet ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Close Association ◽  
Ryanodine Receptors ◽  
Left Ventricular ◽  
Induced Mutations ◽  
Adrenergic Stimulation ◽  
T Tubules ◽  
Junctional Sarcoplasmic Reticulum

Rationale: Ca 2+ -induced Ca 2+ release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules) and RyR (ryanodine receptors) within the junctional sarcoplasmic reticulum. CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. JPH (junctophilin) 2 enables close association between T-tubules and the junctional sarcoplasmic reticulum to ensure efficient CICR. JPH2 has a so-called joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown. Objective: To determine if the joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR. Methods and Results: Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult feline and rat ventricular myocytes. Protein-protein interaction studies showed that the joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the joining region (mut PG1 JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mut PG1 JPH2 caused asynchronous Ca 2+ -release with impaired excitation-contraction coupling after β-adrenergic stimulation. The disturbed Ca 2+ regulation in mut PG1 JPH2 overexpressing myocytes caused calcium/calmodulin-dependent kinase II activation and altered myocyte bioenergetics. Conclusions: The interaction between LTCC and the joining region in JPH2 facilitates dyad assembly and maintains normal CICR in cardiomyocytes.

scholarly journals Localization of Ca2+ + Mg2+-ATPase of the sarcoplasmic reticulum in adult rat papillary muscle.

1982 ◽  
Vol 93 (3) ◽  
pp. 883-892 ◽  
Author(s):  
A O Jorgensen ◽  
A C Shen ◽  
P Daly ◽  
D H MacLennan
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Papillary Muscle ◽  
Functional Role ◽  
Transverse Tubules ◽  
Contraction Coupling ◽  
Adult Rat ◽  
Sarcoplasmic Reticulum Membrane ◽  
Rat Papillary Muscle ◽  
Junctional Sarcoplasmic Reticulum

Localization of the Ca2+ + Mg2+-ATPase of the sarcoplasmic reticulum in rat papillary muscle was determined by indirect immunofluorescence and immunoferritin labeling of cryostat and ultracryotomy sections, respectively. The Ca2+ + Mg2+-ATPase was found to be rather uniformly distributed in the free sarcoplasmic reticulum membrane but to be absent from both peripheral and interior junctional sarcoplasmic reticulum membrane, transverse tubules, sarcolemma, and mitochondria. This suggests that the Ca2+ + Mg2+-ATPase of the sarcoplasmic reticulum is antigenically unrelated to the Ca2+ + Mg2+-ATPase of the sarcolemma. These results are in agreement with the idea that the sites of interior and peripheral coupling between sarcoplasmic reticulum membrane and transverse tubules and between sarcoplasmic reticulum and sarcolemmal membranes play the same functional role in the excitation-contraction coupling in cardiac muscle.

scholarly journals Effects of rogue ryanodine receptors on Ca 2+ sparks in cardiac myocytes

2018 ◽  
Vol 5 (2) ◽  
pp. 171462 ◽  
Author(s):  
Xudong Chen ◽  
Yundi Feng ◽  
Yunlong Huo ◽  
Wenchang Tan
Keyword(s):  
Mathematical Model ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Myocytes ◽  
Ryanodine Receptors ◽  
Experimental Measurements ◽  
Release Mechanisms ◽  
Insight Into ◽  
Junctional Sarcoplasmic Reticulum

Ca 2+ sparks and Ca 2+ quarks, arising from clustered and rogue ryanodine receptors (RyRs), are significant Ca 2+ release events from the junctional sarcoplasmic reticulum (JSR). Based on the anomalous subdiffusion of Ca 2+ in the cytoplasm, a mathematical model was developed to investigate the effects of rogue RyRs on Ca 2+ sparks in cardiac myocytes. Ca 2+ quarks and sparks from the stochastic opening of rogue and clustered RyRs are numerically reproduced and agree with experimental measurements. It is found that the stochastic opening Ca 2+ release units (CRUs) of clustered RyRs are regulated by free Ca 2+ concentration in the JSR lumen (i.e. [Ca 2+ ] lumen ). The frequency of spontaneous Ca 2+ sparks is remarkably increased by the rogue RyRs opening at high [Ca 2+ ] lumen , but not at low [Ca 2+ ] lumen . Hence, the opening of rogue RyRs contributes to the formation of Ca 2+ sparks at high [Ca 2+ ] lumen . The interplay of Ca 2+ sparks and Ca 2+ quarks has been discussed in detail. This work is of significance to provide insight into understanding Ca 2+ release mechanisms in cardiac myocytes.

Differential Ca2+ sensitivity of skeletal and cardiac muscle ryanodine receptors in the presence of calmodulin

2000 ◽  
Vol 279 (3) ◽  
pp. C724-C733 ◽  
Author(s):  
Bradley R. Fruen ◽  
Jennifer M. Bardy ◽  
Todd M. Byrem ◽  
Gale M. Strasburg ◽  
Charles F. Louis
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptors ◽  
Cross Linking ◽  
Release Channel ◽  
Channel Activation ◽  
Functional Interactions ◽  
Ryr2 Channel

Calmodulin (CaM) activates the skeletal muscle ryanodine receptor Ca2+ release channel (RyR1) in the presence of nanomolar Ca2+ concentrations. However, the role of CaM activation in the mechanisms that control Ca2+ release from the sarcoplasmic reticulum (SR) in skeletal muscle and in the heart remains unclear. In media that contained 100 nM Ca2+, the rate of45Ca2+ release from porcine skeletal muscle SR vesicles was increased approximately threefold in the presence of CaM (1 μM). In contrast, cardiac SR vesicle45Ca2+ release was unaffected by CaM, suggesting that CaM activated the skeletal RyR1 but not the cardiac RyR2 channel isoform. The activation of RyR1 by CaM was associated with an approximately sixfold increase in the Ca2+ sensitivity of [3H]ryanodine binding to skeletal muscle SR, whereas the Ca2+ sensitivity of cardiac SR [3H]ryanodine binding was similar in the absence and presence of CaM. Cross-linking experiments identified both RyR1 and RyR2 as predominant CaM binding proteins in skeletal and cardiac SR, respectively, and [35S]CaM binding determinations further indicated comparable CaM binding to the two isoforms in the presence of micromolar Ca2+. In nanomolar Ca2+, however, the affinity and stoichiometry of RyR2 [35S]CaM binding was reduced compared with that of RyR1. Together, our results indicate that CaM activates RyR1 by increasing the Ca2+ sensitivity of the channel, and further suggest differences in CaM's functional interactions with the RyR1 and RyR2 isoforms that may potentially contribute to differences in the Ca2+ dependence of channel activation in skeletal and cardiac muscle.

Role of calmodulin methionine residues in mediating productive association with cardiac ryanodine receptors

2006 ◽  
Vol 290 (2) ◽  
pp. H794-H799 ◽  
Author(s):  
Edward M. Balog ◽  
Laura E. Norton ◽  
David D. Thomas ◽  
Bradley R. Fruen
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptor ◽  
Ryanodine Receptors ◽  
Release Channel ◽  
Site Specific ◽  
High Affinity ◽  
Methionine Residues ◽  
Cardiac Ryanodine Receptor

Calmodulin (CaM) binds to the cardiac ryanodine receptor Ca2+ release channel (RyR2) with high affinity and may act as a regulatory channel subunit. Here we determine the role of CaM Met residues in the productive association of CaM with RyR2, as assessed via determinations of [3H]ryanodine and [35S]CaM binding to cardiac muscle sarcoplasmic reticulum (SR) vesicles. Oxidation of all nine CaM Met residues abolished the productive association of CaM with RyR2. Substitution of the COOH-terminal Mets of CaM with Leu decreased the extent of CaM inhibition of cardiac SR (CSR) vesicle [3H]ryanodine binding. In contrast, replacing the NH2-terminal Met of CaM with Leu increased the concentration of CaM required to inhibit CSR [3H]ryanodine binding but did not alter the extent of inhibition. Site-specific substitution of individual CaM Met residues with Gln demonstrated that Met124 was required for both high-affinity CaM binding to RyR2 and for maximal CaM inhibition. These results thus identify a Met residue critical for the productive association of CaM with RyR2 channels.

scholarly journals Immunoelectron microscopical localization of phospholamban in adult canine ventricular muscle.

1987 ◽  
Vol 104 (5) ◽  
pp. 1343-1352 ◽  
Author(s):  
A O Jorgensen ◽  
L R Jones
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Subcellular Distribution ◽  
Immunogold Labeling ◽  
Relative Distribution ◽  
Ventricular Muscle ◽  
Myocardial Cells ◽  
Microscopical Localization ◽  
Cytoplasmic Side ◽  
Junctional Sarcoplasmic Reticulum

The subcellular distribution of phospholamban in adult canine ventricular myocardial cells was determined by the indirect immunogold-labeling technique. The results presented suggest that phospholamban, like the Ca2+-ATPase, is uniformly distributed in the network sarcoplasmic reticulum but absent from the junctional portion of the junctional sarcoplasmic reticulum. Unlike the Ca2+-ATPase, but like cardiac calsequestrin, phospholamban also appears to be present in the corbular sarcoplasmic reticulum. Comparison of the relative distribution of phospholamban immunolabeling in the sarcoplasmic reticulum with that of the sarcolemma showed that the density of phospholamban in the network sarcoplasmic reticulum was approximately 35-fold higher than that of the cytoplasmic side of the sarcolemma, which in turn was found to be three- to fourfold higher than the density of the background labeling. However, a majority of the specific phospholamban labeling within 30 nm of the cytoplasmic side of the sarcolemma was clustered and present over the sarcoplasmic reticulum in the subsarcolemmal region of the myocardial cells, suggesting that phospholamban is confined to the junctional regions between the sarcolemma and the sarcoplasmic reticulum, but absent from the nonjunctional portion of the sarcolemma. Although the resolution of the immunogold-labeling technique used (60 nm) does not permit one to determine whether the specific labeling within 30 nm of the cytoplasmic side of the sarcolemma is associated with the sarcolemma and/or the junctional sarcoplasmic reticulum, it is likely that the low amount of labeling in this region represents phospholamban associated with sarcoplasmic reticulum. These results suggest that phospholamban is absent from the sarcolemma and confined to the sarcoplasmic reticulum in cardiac muscle.

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