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  • 1
    Electronic Resource
    Electronic Resource
    A comparison of quantitative ultrastructural and contractile characteristics of muscle fibre types of the perch,Perca fluviatilis L. (1985)
    Springer
    Journal of comparative physiology 155 (1985), S. 685-691 
    Details
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Quantitative ultrastructural and physiological parameters were investigated in three types of muscle fibres ofPerca fluviatilis: white fibres from the m. levator operculi anterior, pink (intermediate) fibres of the m. hyohyoideus and deep red fibres of the m. levator operculi anterior. Times to peak tension and half relaxation times of isometric twitches increased in the mentioned order. The extent of contact between the T system and the sarcoplasmic reticulum and the relative volume and surface area of the terminal cisternae showed an inverse relation with the time to peak tension of the twitch. The maximal isometric tetanic force per unit cross section area was similar for all three investigated types. The inverse relation between the time to peak tension of the twitch and the relative length of contact between T system and SR is in agreement with data obtained for fast- and slow twitch muscle fibres of the carp,Cyprinus carpio L.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00694582
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Expression of titin isoforms in red and white muscle fibres of carp (Cyprinus carpio L.) exposed to different sarcomere strains during swimming (1997)
    Springer
    Journal of comparative physiology 167 (1997), S. 543-551 
    Details
    ISSN: 1432-136X
    Keywords: Key words Titin isoforms ; Carp axial muscle ; Gel electrophoresis ; Passive tension ; Passive stiffness ; Fish swimming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Titin (also known as connectin) is a striated-muscle-specific protein that spans the distance between the Z- and M-lines of the sarcomere. The elastic segment of the titin molecule in the I-band is thought to be responsible for developing passive tension and for maintaining the central position of thick filaments in contracting sarcomeres. Different muscle types express isoforms of titin that differ in their molecular mass. To help to elucidate the relation between the occurrence of titin isoforms and the functional properties of different fibre types, we investigated the presence of different titin isoforms in red and white fibres of the axial muscles of carp. Gel electrophoresis of single fibres revealed that the molecular mass of titin was larger in red than in white fibres. Fibres from anterior and posterior axial muscles were also compared. For both white and red fibres the molecular mass of titin in posterior muscle fibres was larger than in anterior muscle fibres. Thus, the same fibre type can express different titin isoforms depending on its location along the body axis. The contribution of titin to passive tension and stiffness of red anterior and posterior fibres was also determined. Single fibres were skinned and the sarcomere length dependencies of passive tension and passive stiffness were determined. Measurements were made before and after extracting thin and thick filaments using relaxing solutions with 0.6 mol · l−1 KCl and 1 mol · l−1 KI. Tension and stiffness measured before extraction were assumed to result from both titin and intermediate filaments, and tension after extraction from only intermediate filaments. Compared to mammalian skeletal muscle, intermediate filaments developed high levels of tension and stiffness in both posterior and anterior fibres. The passive tension-sarcomere length curve of titin increased more steeply in red anterior fibres than in red posterior fibres and the curve reached a plateau at a shorter sarcomere length. Thus, the smaller titin isoform of anterior fibres results in more passive tension and stiffness for a given sarcomere strain. During continuous swimming, red fibres are exposed to larger changes in sarcomere strain than white fibres, and posterior fibres to larger changes in strain than anterior fibres. We propose that sarcomere strain is one of the functional parameters that modulates the expression of different titin isoforms in axial muscle fibres of carp.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050107
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Contractile properties of a white- and a red-fibre type of the m. hyohyoideus of the carp (Cyprinus carpio L.) (1983)
    Springer
    Journal of comparative physiology 149 (1983), S. 441-449 
    Details
    ISSN: 1432-136X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Isometric contraction parameters were measured for white and red fibre bundles isolated from the m. hyohyoideus of the carp. The two fibre types, which have multiterminal innervation, were stimulated via the nerve as well as epimuscularly. Both red and white fibres reacted to a single stimulus with a twitch. Stimulation via the nerve revealed: 1. Twitches and tetani of white fibres have shorter contraction and relaxation times than those of red fibres. 2. Both types reach similar maximal tetanic tensions (about 12 N/cm2) but red fibres require a higher stimulus frequency to reach this tension. 3. The ratio of twitch tension to maximum tetanic tension is 0.42 for white and 0.27 for red fibres. 4. The maximum slope of tension rise in white fibres is independent of the stimulus frequency; in red fibres it increases at high stimulus frequencies. 5. White fibres are more susceptible to fatigue than red fibres. After about 45 s of repeated tetanization (22 tetani) white fibres had lost half their tension. Red fibres had lost half their tension after about 10 min (300 tetani). 6. Sag, the decline of tension during a tetanus, is greater in white than in red fibres. It has a different frequency dependence in both types. 7. Epimuscular stimulation resulted in a slow, incomplete contraction and a very slow decline of tension, especially in red fibres. 8. In agreement with existing biochemical, electromyographical and ultrastructural data, white fibres are adapted for quick short duration activity and red fibres for slow, sustained activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00690001
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  • 4
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    Shortening of the Elastic Tandem Immunoglobulin Segment of Titin Leads to Diastolic Dysfunction [Heart Failure] (2013)
    American Heart Association (AHA)
    Details
    Publication Date: 2013-07-02
    Description: Background— Diastolic dysfunction is a poorly understood but clinically pervasive syndrome that is characterized by increased diastolic stiffness. Titin is the main determinant of cellular passive stiffness. However, the physiological role that the tandem immunoglobulin (Ig) segment of titin plays in stiffness generation and whether shortening this segment is sufficient to cause diastolic dysfunction need to be established. Methods and Results— We generated a mouse model in which 9 Ig-like domains (Ig3–Ig11) were deleted from the proximal tandem Ig segment of the spring region of titin (IG KO). Exon microarray analysis revealed no adaptations in titin splicing, whereas novel phospho-specific antibodies did not detect changes in titin phosphorylation. Passive myocyte stiffness was increased in the IG KO, and immunoelectron microscopy revealed increased extension of the remaining titin spring segments as the sole likely underlying mechanism. Diastolic stiffness was increased at the tissue and organ levels, with no consistent changes in extracellular matrix composition or extracellular matrix–based passive stiffness, supporting a titin-based mechanism for in vivo diastolic dysfunction. Additionally, IG KO mice have a reduced exercise tolerance, a phenotype often associated with diastolic dysfunction. Conclusions— Increased titin-based passive stiffness is sufficient to cause diastolic dysfunction with exercise intolerance.
    Keywords: Other myocardial biology, Other heart failure
    Electronic ISSN: 1524-4539
    Topics: Medicine
    Published by American Heart Association (AHA)
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  • 5
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    IA junction does not control filament length [Biological Sciences] (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-03-18
    Description: We thank Tskhovrebova et al. (1) for allowing us to clarify the conclusions that we drew from our studies. In this work, we genetically targeted a stretch of 14Ig/FnIII domains that comprises the IA junction and revealed that deleting the IA junction moves the attachment point of titin’s spring region...
    Keywords: Letters
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 6
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    Titin's role in muscle structure and function [Physiology] (2014)
    National Academy of Sciences
    Details
    Publication Date: 2014-10-08
    Description: Titin, the largest protein known, forms a giant filament in muscle where it spans the half sarcomere from Z disk to M band. Here we genetically targeted a stretch of 14 immunoglobulin-like and fibronectin type 3 domains that comprises the I-band/A-band (IA) junction and obtained a viable mouse model. Super-resolution...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 7
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    Nebulin deficiency in adult muscle causes sarcomere defects and muscle-type-dependent changes in trophicity: novel insights in nemaline myopathy (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-27
    Description: Nebulin is a giant filamentous protein that is coextensive with the actin filaments of the skeletal muscle sarcomere. Nebulin mutations are the main cause of nemaline myopathy (NEM), with typical adult patients having low expression of nebulin, yet the roles of nebulin in adult muscle remain poorly understood. To establish nebulin's functional roles in adult muscle, we studied a novel conditional nebulin KO (Neb cKO) mouse model in which nebulin deletion was driven by the muscle creatine kinase (MCK) promotor. Neb cKO mice are born with high nebulin levels in their skeletal muscles, but within weeks after birth nebulin expression rapidly falls to barely detectable levels Surprisingly, a large fraction of the mice survive to adulthood with low nebulin levels (〈5% of control), contain nemaline rods and undergo fiber-type switching toward oxidative types. Nebulin deficiency causes a large deficit in specific force, and mechanistic studies provide evidence that a reduced fraction of force-generating cross-bridges and shortened thin filaments contribute to the force deficit. Muscles rich in glycolytic fibers upregulate proteolysis pathways (MuRF-1, Fbxo30 /MUSA1, Gadd45a) and undergo hypotrophy with smaller cross-sectional areas (CSAs), worsening their force deficit. Muscles rich in oxidative fibers do not have smaller weights and can even have hypertrophy, offsetting their specific-force deficit. These studies reveal nebulin as critically important for force development and trophicity in adult muscle. The Neb cKO phenocopies important aspects of NEM (muscle weakness, oxidative fiber-type predominance, variable trophicity effects, nemaline rods) and will be highly useful to test therapeutic approaches to ameliorate muscle weakness.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
    Published by Oxford University Press
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  • 8
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    RLC-P to the rescue [Physiology] (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-07-29
    Description: A common cause of heart failure is hypertrophic cardiomyopathy (HCM) with a prevalence of at least 1 in 500 in adults (1); more recent data suggest that the prevalence of HCM may be as high as 1 in 200 (2). HCM is characterized by disorganized myocyte structure; formation of excess...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Renin overexpression leads to increased titin-based stiffness contributing to diastolic dysfunction in hypertensive mRen2 rats (2016)
    The American Physiological Society (APS)
    Details
    Publication Date: 2016-06-10
    Description: Hypertension (HTN) is a major risk factor for heart failure. We investigated the influence of HTN on cardiac contraction and relaxation in transgenic renin overexpressing rats (carrying mouse Ren-2 renin gene, mRen2, n = 6). Blood pressure (BP) was measured. Cardiac contractility was characterized by echocardiography, cellular force measurements, and biochemical assays were applied to reveal molecular mechanisms. Sprague-Dawley (SD) rats ( n = 6) were used as controls. Transgenic rats had higher circulating renin activity and lower cardiac angiotensin-converting enzyme two levels. Systolic BP was elevated in mRen2 rats (235.11 ± 5.32 vs. 127.03 ± 7.56 mmHg in SD, P 〈 0.05), resulting in increased left ventricular (LV) weight/body weight ratio (4.05 ± 0.09 vs. 2.77 ± 0.08 mg/g in SD, P 〈 0.05). Transgenic renin expression had no effect on the systolic parameters, such as LV ejection fraction, cardiomyocyte Ca 2+ -activated force, and Ca 2+ sensitivity of force production. In contrast, diastolic dysfunction was observed in mRen2 compared with SD rats: early and late LV diastolic filling ratio (E/A) was lower (1.14 ± 0.04 vs. 1.87 ± 0.08, P 〈 0.05), LV isovolumetric relaxation time was longer (43.85 ± 0.89 vs. 28.55 ± 1.33 ms, P 〈 0.05), cardiomyocyte passive tension was higher (1.74 ± 0.06 vs. 1.28 ± 0.18 kN/m 2 , P 〈 0.05), and lung weight/body weight ratio was increased (6.47 ± 0.24 vs. 5.78 ± 0.19 mg/g, P 〈 0.05), as was left atrial weight/body weight ratio (0.21 ± 0.03 vs. 0.14 ± 0.03 mg/g, P 〈 0.05). Hyperphosphorylation of titin at Ser-12742 within the PEVK domain and a twofold overexpression of protein kinase C-α in mRen2 rats were detected. Our data suggest a link between the activation of renin-angiotensin-aldosterone system and increased titin-based stiffness through phosphorylation of titin's PEVK element, contributing to diastolic dysfunction. Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/diastolic-dysfunction-in-the-hypertensive-mren2-rat/ .
    Print ISSN: 0363-6135
    Electronic ISSN: 1522-1539
    Topics: Medicine
    Published by The American Physiological Society (APS)
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  • 10
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    Right Ventricular Diastolic Impairment in Patients With Pulmonary Arterial Hypertension [Hypertension] (2013)
    American Heart Association (AHA)
    Details
    Publication Date: 2013-10-29
    Description: Background— The role of right ventricular (RV) diastolic stiffness in pulmonary arterial hypertension (PAH) is not well established. Therefore, we investigated the presence and possible underlying mechanisms of RV diastolic stiffness in PAH patients. Methods and Results— Single-beat RV pressure-volume analyses were performed in 21 PAH patients and 7 control subjects to study RV diastolic stiffness. Data are presented as mean±SEM. RV diastolic stiffness (β) was significantly increased in PAH patients (PAH, 0.050±0.005 versus control, 0.029±0.003; P 〈0.05) and was closely associated with disease severity. Subsequently, we searched for possible underlying mechanisms using RV tissue of PAH patients undergoing heart/lung transplantation and nonfailing donors. Histological analyses revealed increased cardiomyocyte cross-sectional areas (PAH, 453±31 μm 2 versus control, 218±21 μm 2 ; P 〈0.001), indicating RV hypertrophy. In addition, the amount of RV fibrosis was enhanced in PAH tissue (PAH, 9.6±0.7% versus control, 7.2±0.6%; P 〈0.01). To investigate the contribution of stiffening of the sarcomere (the contractile apparatus of RV cardiomyocytes) to RV diastolic stiffness, we isolated and membrane-permeabilized single RV cardiomyocytes. Passive tension at different sarcomere lengths was significantly higher in PAH patients compared with control subjects (〉200%; P interaction 〈0.001), indicating stiffening of RV sarcomeres. An important regulator of sarcomeric stiffening is the sarcomeric protein titin. Therefore, we investigated titin isoform composition and phosphorylation. No alterations were observed in titin isoform composition (N2BA/N2B ratio: PAH, 0.78±0.07 versus control, 0.91±0.08), but titin phosphorylation in RV tissue of PAH patients was significantly reduced (PAH, 0.16±0.01 arbitrary units versus control, 0.20±0.01 arbitrary units; P 〈0.05). Conclusions— RV diastolic stiffness is significantly increased in PAH patients, with important contributions from increased collagen and intrinsic stiffening of the RV cardiomyocyte sarcomeres.
    Electronic ISSN: 1524-4539
    Topics: Medicine
    Published by American Heart Association (AHA)
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