scholarly journals CaMKII activation in early diabetic hearts induces altered sarcoplasmic reticulum-mitochondria signaling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Marilen Federico ◽  
Maite Zavala ◽  
Tamara Vico ◽  
Sofía López ◽  
Enrique Portiansky ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Control Diet ◽  
Respiratory Control ◽  
Retention Capacity ◽  
Transmission Electron ◽  
Intracellular Ca ◽  
Confocal Images ◽  
Increased Activity ◽  
Camkii Activation

AbstractPrediabetic myocardium, induced by fructose-rich diet (FRD), is prone to increased sarcoplasmic reticulum (SR)-Ca2+ leak and arrhythmias due to increased activity of the Ca2+/calmodulin protein kinase II (CaMKII). However, little is known about the role of SR-mitochondria microdomains, mitochondrial structure, and mitochondrial metabolisms. To address this knowledge gap we measured SR-mitochondrial proximity, intracellular Ca2+, and mitochondrial metabolism in wild type (WT) and AC3-I transgenic mice, with myocardial-targeted CaMKII inhibition, fed with control diet (CD) or with FRD. Confocal images showed significantly increased spontaneous Ca2+ release events in FRD vs. CD WT cardiomyocytes. [3H]-Ryanodine binding assay revealed higher [3H]Ry binding in FRD than CD WT hearts. O2 consumption at State 4 and hydrogen peroxide (H2O2) production rate were increased, while respiratory control rate (RCR) and Ca2+ retention capacity (CRC) were decreased in FRD vs. CD WT isolated mitochondria. Transmission Electron Microscopy (TEM) images showed increased proximity at the SR-mitochondria microdomains, associated with increased tethering proteins, Mfn2, Grp75, and VDAC in FRD vs. CD WT. Mitochondria diameter was decrease and roundness and density were increased in FRD vs. CD WT specimens. The fission protein, Drp1 was significantly increased while the fusion protein, Opa1 was unchanged in FRD vs. CD WT hearts. These differences were prevented in AC3-I mice. We conclude that SR-mitochondria microdomains are subject to CaMKII-dependent remodeling, involving SR-Ca2+ leak and mitochondria fission, in prediabetic mice induced by FRD. We speculate that CaMKII hyperactivity induces SR-Ca2+ leak by RyR2 activation which in turn increases mitochondria Ca2+ content due to the enhanced SR-mitochondria tethering, decreasing CRC.

scholarly journals The calcium stored in the sarcoplasmic reticulum acts as a safety mechanism in rainbow trout heart

2014 ◽  
Vol 307 (12) ◽  
pp. R1493-R1501 ◽  
Author(s):  
Caroline Cros ◽  
Laurent Sallé ◽  
Daniel E. Warren ◽  
Holly A. Shiels ◽  
Fabien Brette
Keyword(s):  
Rainbow Trout ◽  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Adrenergic Stimulation ◽  
Relative Contribution ◽  
Safety Mechanism ◽  
Rapid Changes ◽  
Intracellular Ca ◽  
As Stress

Cardiomyocyte contraction depends on rapid changes in intracellular Ca2+. In mammals, Ca2+ influx as L-type Ca2+ current ( ICa) triggers the release of Ca2+ from sarcoplasmic reticulum (SR) and Ca2+-induced Ca2+ release (CICR) is critical for excitation-contraction coupling. In fish, the relative contribution of external and internal Ca2+ is unclear. Here, we characterized the role of ICa to trigger SR Ca2+ release in rainbow trout ventricular myocytes using ICa regulation by Ca2+ as an index of CICR. ICa was recorded with a slow (EGTA) or fast (BAPTA) Ca2+ chelator in control and isoproterenol conditions. In the absence of β-adrenergic stimulation, the rate of ICa inactivation was not significantly different in EGTA and BAPTA (27.1 ± 1.8 vs. 30.3 ± 2.4 ms), whereas with isoproterenol (1 μM), inactivation was significantly faster with EGTA (11.6 ± 1.7 vs. 27.3 ± 1.6 ms). When barium was the charge carrier, inactivation was significantly slower in both conditions (61.9 ± 6.1 vs. 68.0 ± 8.7 ms, control, isoproterenol). Quantification revealed that without isoproterenol, only 39% of ICa inactivation was due to Ca2+, while with isoproterenol, inactivation was Ca2+-dependent (∼65%) and highly reliant on SR Ca2+ (∼46%). Thus, SR Ca2+ is not released in basal conditions, and ICa is the main trigger of contraction, whereas during a stress response, SR Ca2+ is an important source of cytosolic Ca2+. This was not attributed to differences in SR Ca2+ load because caffeine-induced transients were not different in both conditions. Therefore, Ca2+ stored in SR of trout cardiomyocytes may act as a safety mechanism, allowing greater contraction when higher contractility is required, such as stress or exercise.

scholarly journals Postnatal development and activation of L-type Ca2+ currents in locus ceruleus neurons: implications for a role for Ca2+ in central chemosensitivity

2012 ◽  
Vol 112 (10) ◽  
pp. 1715-1726 ◽  
Author(s):  
Ann N. Imber ◽  
Robert W. Putnam
Keyword(s):  
Postnatal Development ◽  
Respiratory Control ◽  
Locus Ceruleus ◽  
Spike Frequency ◽  
Central Chemosensitivity ◽  
Channel Inhibition ◽  
Strong Linear Correlation ◽  
Intracellular Ca ◽  
Dependent Mechanism

Little is known about the role of Ca2+ in central chemosensitive signaling. We use electrophysiology to examine the chemosensitive responses of tetrodotoxin (TTX)-insensitive oscillations and spikes in neurons of the locus ceruleus (LC), a chemosensitive region involved in respiratory control. We show that both TTX-insensitive spikes and oscillations in LC neurons are sensitive to L-type Ca2+ channel inhibition and are activated by increased CO2/H+. Spikes appear to arise from L-type Ca2+ channels on the soma whereas oscillations arise from L-type Ca2+ channels that are distal to the soma. In HEPES-buffered solution (nominal absence of CO2/HCO3−), acidification does not activate either oscillations or spikes. When CO2 is increased while extracellular pH is held constant by elevated HCO3−, both oscillation and spike frequency increase. Furthermore, plots of both oscillation and spike frequency vs. intracellular [HCO3−]show a strong linear correlation. Increased frequency of TTX-insensitive spikes is associated with increases in intracellular Ca2+ concentrations. Finally, both the appearance and frequency of TTX-insensitive spikes and oscillations increase over postnatal ages day 3–16. Our data suggest that 1) L-type Ca2+ currents in LC neurons arise from channel populations that reside in different regions of the neuron, 2) these L-type Ca2+ currents undergo significant postnatal development, and 3) the activity of these L-type Ca2+ currents is activated by increased CO2 through a HCO3−-dependent mechanism. Thus the activity of L-type Ca2+ channels is likely to play a role in the chemosensitive response of LC neurons and may underlie significant changes in LC neuron chemosensitivity during neonatal development.

scholarly journals Ca2+-ATPase Molecules as a Calcium-Sensitive Membrane-Endoskeleton of Sarcoplasmic Reticulum

2021 ◽  
Vol 22 (5) ◽  
pp. 2624
Author(s):  
Jun Nakamura ◽  
Yuusuke Maruyama ◽  
Genichi Tajima ◽  
Yuto Komeiji ◽  
Makiko Suwa ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Muscle Contraction ◽  
Morphological Changes ◽  
Transmembrane Protein ◽  
Muscle Relaxation ◽  
Transmission Electron ◽  
Almost All ◽  
Induced Crystallization ◽  
Sensitive Membrane

The Ca2+-transport ATPase of sarcoplasmic reticulum (SR) is an integral, transmembrane protein. It sequesters cytoplasmic calcium ions released from SR during muscle contraction, and causes muscle relaxation. Based on negative staining and transmission electron microscopy of SR vesicles isolated from rabbit skeletal muscle, we propose that the ATPase molecules might also be a calcium-sensitive membrane-endoskeleton. Under conditions when the ATPase molecules scarcely transport Ca2+, i.e., in the presence of ATP and ≤ 0.9 nM Ca2+, some of the ATPase particles on the SR vesicle surface gathered to form tetramers. The tetramers crystallized into a cylindrical helical array in some vesicles and probably resulted in the elongated protrusion that extended from some round SRs. As the Ca2+ concentration increased to 0.2 µM, i.e., under conditions when the transporter molecules fully carry out their activities, the ATPase crystal arrays disappeared, but the SR protrusions remained. In the absence of ATP, almost all of the SR vesicles were round and no crystal arrays were evident, independent of the calcium concentration. This suggests that ATP induced crystallization at low Ca2+ concentrations. From the observed morphological changes, the role of the proposed ATPase membrane-endoskeleton is discussed in the context of calcium regulation during muscle contraction.

scholarly journals Refractoriness of sarcoplasmic reticulum Ca2+ release determines Ca2+ alternans in atrial myocytes

2012 ◽  
Vol 302 (11) ◽  
pp. H2310-H2320 ◽  
Author(s):  
Vyacheslav M. Shkryl ◽  
Joshua T. Maxwell ◽  
Timothy L. Domeier ◽  
Lothar A. Blatter
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cellular Level ◽  
Release Mechanism ◽  
Atrial Myocytes ◽  
Restitution Curve ◽  
Intracellular Ca ◽  
Cardiac Alternans ◽  
Kinetics Of ◽  
Beating Frequency

Cardiac alternans is a recognized risk factor for cardiac arrhythmia and sudden cardiac death. At the cellular level, Ca2+ alternans appears as cytosolic Ca2+ transients of alternating amplitude at regular beating frequency. Cardiac alternans is a multifactorial process but has been linked to disturbances in intracellular Ca2+ regulation. In atrial myocytes, we tested the role of voltage-gated Ca2+ current, sarcoplasmic reticulum (SR) Ca2+ load, and restitution properties of SR Ca2+ release for the occurrence of pacing-induced Ca2+ alternans. Voltage-clamp experiments revealed that peak Ca2+ current was not affected during alternans, and alternans of end-diastolic SR Ca2+ load, evaluated by application of caffeine or measured directly with an intra-SR fluorescent Ca2+ indicator (fluo-5N), were not a requirement for cytosolic Ca2+ alternans. Restitution properties and kinetics of refractoriness of Ca2+ release after activation during alternans were evaluated by four different approaches: measurements of 1) the delay (latency) of occurrence of spontaneous global Ca2+ releases and 2) Ca2+ spark frequency, both during rest after a large and small alternans Ca2+ transient; 3) the magnitude of premature action potential-induced Ca2+ transients after a large and small beat; and 4) the efficacy of a photolytically induced Ca2+ signal (Ca2+ uncaging from DM-nitrophen) to trigger additional Ca2+ release during alternans. The results showed that the latency of global spontaneous Ca2+ release was prolonged and Ca2+ spark frequency was decreased after the large Ca2+ transient during alternans. Furthermore, the restitution curve of the Ca2+ transient elicited by premature action potentials or by photolysis-induced Ca2+ release from the SR lagged behind after a large-amplitude transient during alternans compared with the small-amplitude transient. The data demonstrate that beat-to-beat alternation of the time-dependent restitution properties and refractory kinetics of the SR Ca2+ release mechanism represents a key mechanism underlying cardiac alternans.

Store-operated Ca2+ entry modulates sarcoplasmic reticulum Ca2+ loading in neonatal rabbit cardiac ventricular myocytes

2006 ◽  
Vol 290 (6) ◽  
pp. C1572-C1582 ◽  
Author(s):  
Jingbo Huang ◽  
Casey van Breemen ◽  
Kuo-Hsing Kuo ◽  
Leif Hove-Madsen ◽  
Glen F. Tibbits
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Heart Surgery ◽  
Ventricular Myocytes ◽  
Open Heart Surgery ◽  
Cell Types ◽  
Reverse Mode ◽  
Nonselective Cation Channels ◽  
Intracellular Ca ◽  
Neonatal Cardiomyocyte

Store-operated Ca2+ entry (SOCE), which is Ca2+ entry triggered by the depletion of intracellular Ca2+ stores, has been observed in many cell types, but only recently has it been suggested to occur in cardiomyocytes. In the present study, we have demonstrated SOCE-dependent sarcoplasmic reticulum (SR) Ca2+ loading (loadSR) that was not altered by inhibition of L-type Ca2+ channels, reverse mode Na+/Ca2+ exchange (NCX), or nonselective cation channels. In contrast, lowering the extracellular [Ca2+] to 0 mM or adding either 0.5 mM Zn2+ or the putative store-operated channel (SOC) inhibitor SKF-96365 (100 μM) inhibited loadSR at rest. Interestingly, inhibition of forward mode NCX with 30 μM KB-R7943 stimulated SOCE significantly and resulted in enhanced loadSR. In addition, manipulation of the extracellular and intracellular Na+ concentrations further demonstrated the modulatory role of NCX in SOCE-mediated SR Ca2+ loading. Although there is little knowledge of SOCE in cardiomyocytes, the present results suggest that this mechanism, together with NCX, may play an important role in SR Ca2+ homeostasis. The data reported herein also imply the presence of microdomains unique to the neonatal cardiomyocyte. These findings may be of particular importance during open heart surgery in neonates, in which uncontrolled SOCE could lead to SR Ca2+ overload and arrhythmogenesis.

scholarly journals Role of sarcoplasmic reticulum in regulation of tonic contraction of rabbit basilar artery

2001 ◽  
Vol 281 (4) ◽  
pp. H1481-H1489 ◽  
Author(s):  
Tania Szado ◽  
Megan McLarnon ◽  
Xiaodong Wang ◽  
Casey van Breemen
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Basilar Artery ◽  
Cerebral Arteries ◽  
Force Measurements ◽  
Force Development ◽  
Plasmic Reticulum ◽  
Intracellular Ca ◽  
Subsequent Addition ◽  
Measuring Force

Superficial sarcoplasmic reticulum (SR) regulates smooth muscle force development directly by Ca2+ release and removal to and from the cytoplasm (Somlyo and Somlyo. J Cardiovasc Pharmacol 8, Suppl8: S42–S47, 1986) by buffering Ca2+ influx and contributing to Ca2+ extrusion (Mueller and van Breemen. Nature 281: 682–683, 1979) and indirectly by releasing Ca2+ near Ca2+-activated K+channels (KCa) to hyperpolarize the plasma membrane (Bolton and Imaizumi. Cell Calcium 20: 141–152, 1996 and Nelson et al. Science 270: 633–637, 1995). In the rabbit basilar artery, relative contributions of direct effects and those mediated through activation of KCa were evaluated by measuring force and intracellular Ca2+ concentration ([Ca2+]i) in response to the SR-depleting agents thapsigargin and ryanodine and the large conductance KCa (BKCa) blockers iberiotoxin (IbTX) and tetraethylammonium ion (TEA). A large contraction was observed in response to KCa blockade with either 3 mM TEA or 100 nM IbTX and also after addition of 10 μM ryanodine or 2 μM thapsigargin. When KCa was blocked first with TEA or IbTX, subsequent addition of thapsigargin or ryanodine also increased force. Measurements of fura 2 fluorescence showed parallel increases in [Ca2+]i in response to sequential blockade of sarco(endo)plasmic reticulum Ca2+-ATPase and KCa regardless of the order of application. It appears that a significant fraction of KCa remains activated in the absence of SR function and that SR contributes to relaxation after blockade of KCa. We found that depletion of SR before stimulating Ca2+ influx through voltage-gated Ca2+ channels markedly reduced force development rate and that thapsigargin abolished this effect. We conclude that the SR of rabbit cerebral arteries modulates constriction by direct and indirect mechanisms.

scholarly journals Role of P 2 receptors in Cerebral Vasospasm

Stroke ◽  
2001 ◽  
Vol 32 (suppl_1) ◽  
pp. 354-355
Author(s):  
John H Zhang ◽  
Hitoshi Kimura ◽  
Robin Carpenter ◽  
Andrew D Parent
Keyword(s):  
Receptor Antagonist ◽  
Mrna Expression ◽  
Cerebral Vasospasm ◽  
Cerebral Arteries ◽  
Control Group ◽  
Arterial Blood ◽  
Transmission Electron ◽  
Intracellular Ca ◽  
Basilar Arteries

P87 Introduction: Extracellular ATP activates P 2 receptors to increase intracellular Ca 2+ , to contract cerebral arteries, and to induce vasospasm in animals. This study examined the mRNA expression of P 2 receptors in a rat double hemorrhage model and explored the therapeutic role of P 2 receptor antagonists in a dog double hemorrhage model. Methods: One hundred SD rats were divided into five groups to undergo double hemorrhage by injecting autologous arterial blood into cisterna magna on day 0 and 2. Rats were sacrificed on day 3, 5 or 7. In sham group, rats were injected with saline. In control group, no surgery was conducted. Basilar arteries were harvested for mRNA isolation and RT-PCR or were fixed for transmission electron microscopy (TEM). Eighteen dogs were divided into three groups to have double hemorrhage and sacrificed on day 7. Two groups were treated, intracisternally, with P 2 receptor antagonist suramin (selective for P 2Y and P 2X ) or PPADS (selective for P 2X1 ) (30 μM) from day 3–6. Angiograph was performed before blood injection and before sacrifice. The basilar arteries were collected for TEM. Results: Mild to moderate vasospasm (30–40% reduction) was observed on day 3–7 in rats. The mRNA expression of P 2X1 receptor was down-regulated (P<0.05) on day 3 and recovered on day 5 and 7. P 2Y1 and P 2Y2 receptors were up-regulated (P<0.05) on day 5 and remain elevated on day 7. No changes were observed in the shame group. Severe vasospasm was observed on day 7 in dogs. P 2 receptor antagonist Suramin but not PPADS significantly reversed (P<0.01, ANOVA) vasospasm in dogs. Discussion: P 2Y1 and P 2Y2 , but not P 2X1 , may be involved in cerebral vasospasm. Up-regulation of P 2Y receptor may enable ATP to produce contraction at low concentrations. Suramin reduced vasospasm probably by blocking P 2Y receptors.

A Reproducible Selective Stain for Cardiac Sarcoplasmic Reticulum

1974 ◽  
Vol 32 ◽  
pp. 214-215
Author(s):  
R. A. Waugh ◽  
J. R. Sommer
Keyword(s):  
Complex System ◽  
Electron Microscope ◽  
Sarcoplasmic Reticulum ◽  
Transmission Electron Microscope ◽  
Electron Microscopic ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Transmission Electron

Cardiac sarcoplasmic reticulum (SR) is a complex system of intracellular tubules that, due to their small size and juxtaposition to such electron-dense structures as mitochondria and myofibrils, are often inconspicuous in conventionally prepared electron microscopic material. This study reports a method with which the SR is selectively “stained” which facilitates visualizationwith the transmission electron microscope.

On Future Directions in Pathology

1982 ◽  
Vol 40 ◽  
pp. 274-277
Author(s):  
Benjamin F. Trump ◽  
Irene K. Berezesky ◽  
Raymond T. Jones
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Clinical Pathology ◽  
Future Directions ◽  
Diagnostic Pathology ◽  
The Past ◽  
Transmission Electron ◽  
Organ Systems ◽  
The Many

The role of electron microscopy and associated techniques is assured in diagnostic pathology. At the present time, most of the progress has been made on tissues examined by transmission electron microscopy (TEM) and correlated with light microscopy (LM) and by cytochemistry using both plastic and paraffin-embedded materials. As mentioned elsewhere in this symposium, this has revolutionized many fields of pathology including diagnostic, anatomic and clinical pathology. It began with the kidney; however, it has now been extended to most other organ systems and to tumor diagnosis in general. The results of the past few years tend to indicate the future directions and needs of this expanding field. Now, in addition to routine EM, pathologists have access to the many newly developed methods and instruments mentioned below which should aid considerably not only in diagnostic pathology but in investigative pathology as well.

Transmission Electron Microscopy studies of texture of Cr underlayer of magnetic recording hard disk

1991 ◽  
Vol 49 ◽  
pp. 580-581
Author(s):  
L. Tang ◽  
G. Thomas ◽  
M. R. Khan ◽  
S. L. Duan
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Transmission Electron Microscopy ◽  
Magnetic Recording ◽  
Magnetic Thin Films ◽  
Magnetic Films ◽  
Substrate Bias ◽  
Epitaxial Relationship ◽  
Transmission Electron

Cr thin films are often used as underlayers for Co alloy magnetic thin films, such as Co1, CoNi2, and CoNiCr3, for high density longitudinal magnetic recording. It is belived that the role of the Cr underlayer is to control the growth and texture of the Co alloy magnetic thin films, and, then, to increase the in plane coercivity of the films. Although many epitaxial relationship between the Cr underlayer and the magnetic films, such as ﹛1010﹜Co/ {110﹜Cr4, ﹛2110﹜Co/ ﹛001﹜Cr5, ﹛0002﹜Co/﹛110﹜Cr6, have been suggested and appear to be related to the Cr thickness, the texture of the Cr underlayer itself is still not understood very well. In this study, the texture of a 2000 Å thick Cr underlayer on Nip/Al substrate for thin films of (Co75Ni25)1-xTix dc-sputtered with - 200 V substrate bias is investigated by electron microscopy.

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