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PubMed1992

Purification and characterization of nebulin subfragments produced by 0.1 mM CaCl2.

Nebulin, which forms a long inextensible filament in sarcomeres, was fragmented into 200-, 180-, 40-, 33-, and 23-kDa subfragments on treatment with 0.1 mM CaCl2. The subfragments released from myofibrils were successfully purified by immunoaffinity column chromatography. The 200-, 40-, 33-, and 23-kDa subfragments were released from myofibrils and occupied 80% of the nebulin filaments. The remainder comprised the 180-kDa subfragment bound to the myofibrils. There is a possibility that an entire nebulin filament is constructed from the 200-, 180-, 40-, 33-, and 23-kDa subfragments. We have developed a new "fluorescence-method" to detect the binding of calcium ions to a protein using quin2, and clarified that nebulin is a calcium-binding protein, and that calcium ions bind to the 200-, 40-, and 23-kDa subfragments. Nebulin filaments are probably fragmented on the binding of large amounts of calcium ions to the 200-, 40-, and 23-kDa subfragments.

Amino Acids↗
PubMed1977

I-protein a new regulatory protein from vertebrate skeletal muscle. II. Localization.

Rabbit antiserum raised agains I-protein was used for immunofluorescent staining of chicken myofibrils. The FITC-conjugated anti-I-protein antibody stained A-band regions except at their middle regions. According to the conditions used, the myofibrils stained by their fluorescent antibody showed slightly different patterns, i.e., the nonstained regions in the center of the A-bands were wider. On fixing with glutaraldehyde, myofibrils were stained in the A-band regions except at their middle regions. Therefore, I-protein may be localized at A-bands except for the center.

Animals↗
PubMed1982

Identification of Drosophila indirect flight muscle myofibrillar proteins by means of two-dimensional electrophoresis.

When proteins of whole Drosophila thorax were analyzed by two-dimensional gel electrophoresis, 186 spots were detected by protein staining with Coomassie brilliant blue R-250. Two methods were developed to identify proteins which exist in indirect flight muscle (IFM) and its myofibrils. 1) A whole fly was freeze-dried in a dry ice-acetone mixture, and indirect flight muscle fibers were cleanly dissected out from the thorax. The muscle cells and the rest of the thorax were analyzed separately. The muscle contained 146 polypeptides, of which 12 were not detected elsewhere. 2) Flies were frozen in liquid nitrogen and shaken vigorously so that their thoraces broke off from heads and abdomens. The thoraces were separated from the rest by sieving and centrifugation. After homogenization of the thorax, myofibrils were prepared by centrifugation in a discontinuous sucrose density gradient. The myofibril fraction contained at least 20 proteins. There were two types of actin (II and III), myosin heavy chain, tropomyosin and paramyosin. Nine of the other myofibrillar proteins were specific to this muscle.

Animals↗
PubMed2006

Propofol decreases myofilament Ca2+ sensitivity via a protein kinase C-, nitric oxide synthase-dependent pathway in diabetic cardiomyocytes.

BACKGROUND: The authors' objective was to assess the role of protein kinase C (PKC) and nitric oxide synthase (NOS) in mediating the effects of propofol on diabetic cardiomyocyte contractility, intracellular free Ca2+ concentration ([Ca2+]i), and myofilament Ca2+ sensitivity. METHODS: Freshly isolated ventricular myocytes were obtained from normal and diabetic rat hearts. [Ca2+]i and cell shortening were simultaneously measured in electrically stimulated, ventricular myocytes using fura-2 and video-edge detection, respectively. Actomyosin adenosine triphosphatase activity and troponin I (TnI) phosphorylation were assessed in [32P]orthophosphate-labeled myofibrils. Western blot analysis was used to assess expression of PKC and NOS. RESULTS: Propofol (10 microM) decreased peak shortening by 47 +/- 6% with little effect on peak [Ca2+]i (92 +/- 5% of control) in diabetic myocytes. Maximal actomyosin adenosine triphosphatase activity was reduced by 43 +/- 7% and TnI phosphorylation was greater (32 +/- 6%) in diabetic myofibrils compared with normal. Propofol reduced actomyosin adenosine triphosphatase activity by 17 +/- 7% and increased TnI phosphorylation in diabetic myofibrils. PKC inhibition prevented the propofol-induced increase in TnI phosphorylation and decrease in shortening. Expression of PKC-alpha, PKC-delta, PKC-epsilon, and constitutive NOS were up-regulated and inducible NOS was expressed in diabetic cardiomyocytes. NOS inhibition attenuated the propofol-induced decrease in shortening. CONCLUSION: Myofilament Ca2+ sensitivity and, to a lesser extent, peak [Ca2+]i are decreased in diabetic cardiomyocytes. Increases in PKC and NOS expression in combination with TnI phosphorylation seem to contribute to the decrease in [Ca2+]i and myofilament Ca2+ sensitivity. Propofol decreases [Ca2+]i and shortening via a PKC-, NOS-dependent pathway.

Actin Cytoskeleton↗
PubMed1996

Myofibrillar myopathy with abnormal foci of desmin positivity. II. Immunocytochemical analysis reveals accumulation of multiple other proteins.

The two major types of lesions in myofibrillar myopathy consist of hyaline spheroidal structures composed of compacted myofibrillar residues, and nonhyaline lesions that comprise foci of myofibrillar destruction. We employed immunocytochemical analysis to further characterize these abnormalities. The nonhyaline lesions are depleted of actin, alpha-actinin, myosin, and, less consistently, of titin and nebulin. Thus, each major component of the myofibrils is lost or decreased. These lesions also react strongly for both NCAM and desmin. By contrast, the hyaline structures are highly enriched in actin, are immunoreactive for fast and slow myosin, and show increased expression of titin, nebulin, and alpha-actinin. They fail to react for NCAM and react variably for desmin. Both types of lesion react, but with differing intensities, for gelsolin, dystrophin, beta-amyloid precursor protein (beta APP) epitopes amino-terminal to the alpha-secretase site, alpha 1-antichymotrypsin, and ubiquitin, and both can be congophilic. The increased expressions of desmin, dystrophin and gelsolin in muscle are also confirmed by immunoblot studies. The results, in harmony with the ultrastructural findings described in the companion paper, suggest that myofibrillar myopathy is conditioned by abnormal activation of a degradative process that primarily affects the myofibrils. A structural abnormality of desmin alone may not be sufficient to disrupt the myofibrillar architecture, but abnormal activation of a phosphorylating process could account for dissolution of the myofibrils. The cause and significance of the ectopic overexpression of desmin, dystrophin, NCAM, and beta APP components, and the chemical basis of the congophilia remain unknown.

Actins↗
PubMed2006

Evolution of long-range myofibrillar crystallinity in insect flight muscle as examined by X-ray cryomicrodiffraction.

Insect flight muscle is known for its crystal-quality regularity of contractile protein arrangement within a sarcomere. We have previously shown by X-ray microdiffraction that the crystal-quality regularity in bumble-bee flight muscle is not confined within a sarcomere, but extends over the entire length of a myofibril (>1000 sarcomeres connected in series). Because of this, the whole myofibril may be regarded as a millimetre-long, natural single protein crystal. Using bright X-ray beams from a synchrotron radiation source, we examined how this long-range crystallinity has evolved among winged insects. We analysed >4600 microdiffraction patterns of quick-frozen myofibrils from 50 insect species, covering all the major winged insect orders. The results show that the occurrence of such long-range crystallinity largely coincides with insect orders with asynchronous muscle operation. However, a few of the more skilled fliers among lower-order insects apparently have developed various degrees of structural regularity, suggesting that the demand for skillful flight has driven the lattice structure towards increased regularity.

Animals↗
PubMed1984

Precardiac mesoderm differentiation in vitro. Actin-isotype synthetic transitions, myofibrillogenesis, initiation of heartbeat, and the possible involvement of collagen.

The differentiation of precardiac mesoderm into beating heart tissue was examined during explant culture. Explanted tissue forms tubular heart-like vesicles and initiates rhythmic contractility within 18-24 h in vitro, a developmental time-course approximating that observed during in vivo development. Electron-microscopic observations reveal that beating heart cells are rich in cytoplasmic myofibrils in varying degrees of order, with some regions containing highly organized myofibrillar arrays. The analysis of actin-isotype biosynthesis, using metabolic labeling with [35S]-methionine and isoelectric-focusing resolution of the synthesized radioactive polypeptides, demonstrates that the initiation of cardiac alpha-actin synthesis and the pattern of transition in the synthesis of alpha-, beta-, and gamma-actin isotypes is equivalent to the initiation time and pattern observed in vivo. A possible collagen involvement in the differentiation process was investigated by assessing the effects of collagen-synthesis inhibitors on the development of the explant cultures. Two different agents, alpha, alpha'-dipyridyl and L-azetidine-2-carboxylic acid, exhibited a dose-dependent ability to inhibit the formation of beating heart tissue. When examined by electron microscopy, the nonbeating tissue exhibited a drastic depression of myofibrillogenesis, but otherwise appeared healthy. Further examination of the effect of L-azetidine-2-carboxylic acid demonstrated that the inhibition of myofibril formation and heartbeat was correlated with a 60% inhibition of native collagen synthesis; however, the time-course and pattern of actin-isotype biosynthesis was completely unaffected. The data suggest a possible involvement in heart differentiation that is necessary for either the synthesis of non-actin cardiac contractile proteins or the assembly of cardiac contractile proteins into myofibrils.

Actins↗
PubMed1990

Binding of ADP and adenosine 5'-[beta, gamma-imido]triphosphate to insect flight muscle fibrils.

We have studied the binding of ADP and adenosine 5'-[beta, gamma-imido]triphosphate (AdoPP[NH]P) to insect flight muscle fibrils. We find that 25% of the myosin heads, presumably those which do not interact with actin, bind AdoPP[NH]P with a binding constant greater than 3 X 10(6) M-1, similar to the binding constant of the same compound to the rabbit myosin heads which do not overlap with actin. The remaining heads in insect myofibrils bind AdoPP[NH]P with an association constant of 8 X 10(3) M-1, which is eight times stronger than the affinity of this compound for rabbit myosin heads in overlap with actin. Therefore, in contrast to the situation with rabbit myofibrils where AdoPP[NH]P binds much more weakly than ADP, with insect myofibrils these two adenosine phosphates bind with almost equal affinity. This is consistent with the numerous structural studies on insect flight muscle which were interpreted on the basis that most of the actomyosin sites were saturated with nucleotide at an AdoPP[NH]P concentration of 1 mM.

Adenosine Diphosphate↗
PubMed1985

The intermediate filament protein desmin in cardiac and skeletal muscle from normal and dystrophic (BIO 14.6) hamsters.

Electrophoretic separation on polyacrylamide gels of polypeptides extracted from skeletal and cardiac muscle of BIO 14.6 dystrophic, carrier, and random-bred normal hamsters demonstrates similar quantities and electrophoretic mobility of a protein having a relative mass of 52 000 daltons (apparent isoelectric point 6.2) from all sources examined; we have tentatively identified this protein as the intermediate filament protein desmin. Reaction of such separated polypeptides transferred to nitrocellulose blots with antibodies raised against this protein fails to show immunological differences in this 52 000 dalton protein in cardiac and skeletal muscle from normal and dystrophic animals. Indirect immunofluorescence analysis of skeletal myofibrils from 30-to 60-day normal and dystrophic animals shows no differences in Z-line staining when immunoglobulins from anti-alpha-actinin serum are used as primary antibodies. Immunoglobulins from the putative anti-desmin serum also produce Z-line staining of skeletal myofibrils from normal animals, but fail to bind to the Z-lines of some skeletal myofibrils from dystrophic hamsters.

Animals↗
PubMed2002

HSC73-tubulin complex formation during low-flow ischemia in the canine myocardium.

Canine myocardium was exposed to bouts of low-flow ischemia to identify the interactions that develop between the microtubule-based cytoskeleton and the heat shock protein 70 (HSP70) family of heat shock proteins in viable cardiomyocytes. "Moderate" or "severe" low-flow ischemia was produced in chronically instrumented dogs by reducing circumflex coronary flow by 50% for 2 h or by 75% for 5 h followed by reperfusion for 2 and 24 h, respectively. Electron and immunofluorescence microscopy demonstrated either partial or nearly complete depolymerization of the intermyofibrillar microtubules in areas of myofibril disruption and partial dissolution of the perinuclear microtubule girdle. In contrast, centrosomal tubulin arrays appeared to remain intact following low-flow ischemia. In cardiomyocytes displaying myofibril disruption, constitutively expressed HSP73 (HSC73) colocalized with intact but not disrupted microtubules and with perinuclear and centrosomal tubulin following moderate ischemia. Microtubule depolymerization and high molecular weight tubulin-HSC73 complexes were present in more severely ischemic tissue. These results suggest that HSC73 directly interacts with tubulin and may protect selected elements of the microtubule network and limit myofibril disruption during reversible low-flow ischemia.

Animals↗
PubMed1983

Swimming exercise, thyroid state, and the distribution of myosin isoenzymes in rat heart.

We tested whether changes in cardiac myosin ATPase activity induced by swimming exercise in male rats are due to a redistribution of existing isoenzymic forms of ventricular myosin. The isoenzymic profiles were analyzed by nondissociating gel electrophoresis of ventricular samples and compared with ATPase activities of myofibrils prepared from the same ventricle. Myofibrils prepared from hearts of rats in the control sedentary group or from hearts of rats in the groups of 8- or 12-wk swimmers had the same actomyosin Mg2+-ATPase activities measured between pCa 8 and 5. However, the myosin Ca2+-ATPase activity of myofibrils prepared from hearts of 8- or 12-wk swimmers was 20% higher than the activity of control preparations. This increase in activity was in proportion to an increase in the relative amount of V1, the myosin isoenzyme with the highest Ca2+-ATPase activity. Thyroidectomized rats, whose hearts had no detectable V1, were also subjected to the swimming program. In the case of the hypothyroid rats, myofibrillar preparations from controls and 8- or 12-wk swimmers had the same actomyosin Mg2+-ATPase activity, myosin Ca2+-ATPase activity, and the same isoenzyme profiles. Co-electrophoresis of ventricular samples from the euthyroid and hypothyroid controls and swimmers showed no evidence for new variants of myosin. We conclude that the increase in myosin Ca2+-ATPase activity in the ventricles of euthyroid swimmers is due to a redistribution of existing isoforms of myosin and that the redistribution process may require thyroid hormone for its expression.

Actomyosin↗
PubMed1978

Adaptation of the rat myocardium to endurance training.

The purpose of this study was to assess cardiac adaptation to endurance training in rats. After 11 wk of progressive treadmill exercise (1 h/day), gastrocnemius cytochrome c oxidase activity was 38% higher (P less than 0.01) in the trained (n = 20) as compared to control (n = 20) rats. Cardiac Mg2+-stimulated myofibril ATPase activity (0.308 +/- 0.012 vs. 0.324 +/- 0.006 micrometer.mg-1.min-1) did not change nor was there any change in myofibril protein concentration (60.0 +/- 1.12 vs. 59.9 +/- 0.85 mg.g-1). The isolated left ventricular papillary muscle showed no significant change in time-to-peak tension (TPT) or half-relaxation time. Tension output, however, was significantly increased with training, 2.2 +/- 0.3 vs. 1.5 +/- 0.1 g.mm-2 (P less than 0.025). Furthermore, when the papillary preparations were perfused with 0.5 mM lanthanum (La3+) to displace membrane-bound Ca2+, the time course for tension decay was significantly prolonged in the trained muscles (P less than 0.001). We conclude that endurance running of this type does not necessarily increase myofibril ATPase activity or the time course of the isometric twitch of rat papillary muscle. However, tension output per unit area does increase and this appears to be due to a greater amount of Ca2+ being made available to the contractile apparatus.

Adaptation, Physiological↗
PubMed2005

Isometric resistance exercise fails to counteract skeletal muscle atrophy processes during the initial stages of unloading.

This study tested the hypothesis that an isometric resistance training paradigm targeting the medial gastrocnemius of adult rodents is effective in preventing muscle atrophy during the early stages of hindlimb unloading by maintaining normal activation of the insulin receptor substrate-1 (IRS-1)/phosphoinositide-3 kinase (PI3K)/Akt signaling pathway. This pathway has been shown to simultaneously create an anabolic response while inhibiting processes upregulating catabolic processes involving expression of key enzymes in the ubiquitination of proteins for degradation. The findings show that during the 5 days of unloading 1) absolute medial gastrocnemius muscle weight reduction occurred by approximately 20%, but muscle weight corrected to body weight was not different from normal weight-bearing controls (P < 0.05); 2) normalized myofibril fraction concentration and content were decreased; and 3) a robust isometric training program, known to induce a hypertrophy response, failed to maintain the myofibril protein content. This response occurred despite fully blunting the increases in the mRNA for of atrogin-1, MURF-1, and myostatin, e.g., sensitive gene markers of an activated catabolic state. Analyses of the IRS-1/PI3K/Akt markers indicated that abundance of IRS-1 and phosphorylation state of Akt and p70S6 kinase were decreased relative to normal control rats, and the resistance training failed to maintain these signaling markers at normal regulatory level. Our findings suggest that to fully prevent muscle atrophy responses affecting the myofibril system during unloading, the volume of mechanical stress must be augmented sufficiently to maintain optimal activity of the IRS-1/PI3K/Akt pathway to provide an effective anabolic stimulus on the muscle.

Animals↗
PubMed2006

Impaired diastolic function after exchange of endogenous troponin I with C-terminal truncated troponin I in human cardiac muscle.

The specific and selective proteolysis of cardiac troponin I (cTnI) has been proposed to play a key role in human ischemic myocardial disease, including stunning and acute pressure overload. In this study, the functional implications of cTnI proteolysis were investigated in human cardiac tissue for the first time. The predominant human cTnI degradation product (cTnI(1-192)) and full-length cTnI were expressed in Escherichia coli, purified, reconstituted with the other cardiac troponin subunits, troponin T and C, and subsequently exchanged into human cardiac myofibrils and permeabilized cardiomyocytes isolated from healthy donor hearts. Maximal isometric force and kinetic parameters were measured in myofibrils, using rapid solution switching, whereas force development was measured in single cardiomyocytes at various calcium concentrations, at sarcomere lengths of 1.9 and 2.2 mum, and after treatment with the catalytic subunit of protein kinase A (PKA) to mimic beta-adrenergic stimulation. One-dimensional gel electrophoresis, Western immunoblotting, and 3D imaging revealed that approximately 50% of endogenous cTnI had been homogeneously replaced by cTnI(1-192) in both myofibrils and cardiomyocytes. Maximal tension was not affected, whereas the rates of force activation and redevelopment as well as relaxation kinetics were slowed down. Ca(2+) sensitivity of the contractile apparatus was increased in preparations containing cTnI(1-192) (pCa(50): 5.73+/-0.03 versus 5.52+/-0.03 for cTnI(1-192) and full-length cTnI, respectively). The sarcomere length dependency of force development and the desensitizing effect of PKA were preserved in cTnI(1-192)-exchanged cardiomyocytes. These results indicate that degradation of cTnI in human myocardium may impair diastolic function, whereas systolic function is largely preserved.

Cyclic AMP-Dependent Protein Kinases↗
PubMed1981

Myocardial morphometric characteristics in swine.

We have quantified the ultrastructure of myocardial cells in tissue samples obtained from six adult normal Yucatan swine. Tissue samples were obtained from 20 different sites in the left ventricle, right ventricle, and interventricular septum. The samples were processed for electron microscopy and quantitative morphometric analysis. The percent relative volumes of myofibrils, mitochondria, transverse tubular system, sarcoplasmic reticulum, and clear intracellular space were determined using stereological morphometric methods. Overall, the data were distributed homogeneously among the 20 individual sites. However, when certain subcellular components were examined regionally, some differences appeared. The mitochondrial:myofibril volume ratios were significantly increased in the left ventricle and interventricular septum compared to the right ventricle. They also were greater in the endocardial region compared to the epicardium, which is consistent with higher metabolic activity of these zones. Similarly, the sarcoplasmic reticulum:myofibril ratio was greater in the endocardial region vs. the epicardial region and the basal layer compared to the mid-layer, suggesting the greater need for provision of calcium ions in these particular zones. Since the swine is a convenient large animal for physiological studies, the results indicate that swine can also be used for quantitative morphometric measurements of myocardial changes in normal and pathologic hearts, and for the study of regional changes in various layers and regions of heart walls.

Animals↗
PubMed1987

Induction of myofibrillogenesis in cardiac lethal mutant axolotl hearts rescued by RNA derived from normal endoderm.

A strain of axolotl, Ambystoma mexicanum, that carries the cardiac lethal or c gene presents an excellent model system in which to study inductive interactions during heart development. Embryos homozygous for gene c contain hearts that fail to beat and do not form sarcomeric myofibrils even though muscle proteins are present. Although they can survive for approximately three weeks, mutant embryos inevitably die due to lack of circulation. Embryonic axolotl hearts can be maintained easily in organ culture using only Holtfreter's solution as a culture medium. Mutant hearts can be induced to differentiate in vitro into functional cardiac muscle containing sarcomeric myofibrils by coculturing the mutant heart tube with anterior endoderm from a normal embryo. The induction of muscle differentiation can also be mediated through organ culture of mutant heart tubes in medium 'conditioned' by normal anterior endoderm. Ribonuclease was shown to abolish the ability of endoderm-conditioned medium to induce cardiac muscle differentiation. The addition of RNA extracted from normal early embryonic anterior endoderm to organ cultures of mutant hearts stimulated the differentiation of these tissues into contractile cardiac muscle containing well-organized sarcomeric myofibrils, while RNA extracted from early embryonic liver or neural tube did not induce either muscular contraction or myofibrillogenesis. Thus, RNA from anterior endoderm of normal embryos induces myofibrillogenesis and the development of contractile activity in mutant hearts, thereby correcting the genetic defect.

Ambystoma↗
PubMed2004

Chaperone-mediated folding and assembly of myosin in striated muscle.

De novo folding and assembly of striated muscle myosin was analyzed by expressing a GFP-tagged embryonic myosin heavy chain (GFP-myosin) in post-mitotic C2C12 myocytes using replication defective adenoviruses. In the early stages of muscle differentiation, the GFP-myosin accumulates in bright globular foci and short filamentous structures that are later replaced by brightly fluorescent myofibrils. Time-lapse microscopy shows that the intermediates are dynamic and are present in elongating and fusing myocytes and in multinucleated myotubes. Immunostaining reveals the co-localization of the molecular chaperones Hsc70 and Hsp90 with the GFP-myosin in the intermediates, but not in the mature myofibrils. Uninfected cells have similar intermediates suggesting a common pathway for myosin maturation. Two conformation-sensitive antibodies that bind the unfolded motor domain and the coiled-coil conformation of the rod demonstrate that in the intermediates, the myosin rod is folded but the motor domain is not folded. Electron microscopy reveals that the intermediates contain loose filament bundles surrounded by a protein rich matrix. Geldanamycin, a specific inhibitor of Hsp90, reversibly blocks myofibril assembly and triggers accumulation of myosin folding intermediates. We conclude that multimeric complexes of nascent myosin filaments associated with Hsc70 and Hsp90 are intermediates in the folding and assembly pathway of muscle myosin.

Adenoviridae Infections↗
PubMed1999

Myofibrillogenesis in the developing chicken heart: assembly of Z-disk, M-line and the thick filaments.

Myofibrillogenesis in situ was investigated by confocal microscopy of immunofluorescently labelled whole mount preparations of early embryonic chicken heart rudiments. The time-course of incorporation of several components into myofibrils was compared in triple-stained specimens, taken around the time when beating starts. All sarcomeric proteins investigated so far were already expressed before the first contractions and myofibril assembly happened within a few hours. No typical stress fibre-like structures or premyofibrils, structures observed in cultured cardiomyocytes, could be detected during myofibrillogenesis in the heart. Sarcomeric proteins like (&agr;)-actinin, titin and actin were found in a defined localisation pattern even in cardiomyocytes that did not yet contain myofibrils, making up dense body-like structures. As soon as the heart started to beat, all myofibrillar proteins were already located at their exact position in the sarcomere. The maturation of the sarcomeres was characterised by a short delay in the establishment of the pattern for M-line epitopes of titin with respect to Z-disk epitopes and the incorporation of the M-line component myomesin, which preceded that of myosin binding protein-C. Thus dense body-like structures, made up of titin, (&agr;)-actinin and actin filaments serve as the first organised complexes also during myofibrillogenesis in situ and titin functions as a ruler for sarcomere assembly as soon as its C termini have become localised. We suggest that assembly of thin and thick filament occurs independently during myofibrillogenesis in situ and that myomesin might be important for integrating thick filaments with the M-line end of titin.

Animals↗