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At least 397 records · Page 22Linked to original sources
PubMed1998

Liberation of phospholipids from Z-disks of chicken skeletal muscle myofibrils by 0.1 mM calcium ions: weakening mechanism for Z-disks during post-mortem aging of meat.

Weakening of the Z-disks of skeletal muscle myofibrils contributes to the tenderization of meat during post-mortem aging. To elucidate the weakening mechanism, we compared Z-disks weakened by post-mortem aging of chicken breast muscle with those of myofibrils treated with a solution containing 0.1 mM CaCl2 and 1 microM calpastatin domain I. In both cases, the Z-disks were weakened with a corresponding liberation of their constituent phospholipids (PLs). The liberation of PLs specific to 0.1 mM calcium ions was minimal at pH 6.5 and maximal at 35 degrees C together with the Z-disk weakening. Binding of calcium ions to PLs in the Z-disks was determined by 45Ca-autoradiography. Acidic PLs were strongly radioactive and neutral PLs were appreciably radioactive. It is very probable that acidic PLs would bind electrostatically to alpha-actinin under physiological conditions, and that this interaction would be broken by the binding of calcium ions at 0.1 mM to PLs, resulting in the partial liberation of PLs from Z-disks. We conclude, therefore, that the liberation of PLs by the binding of 0.1 mM calcium ions was the main cause for Z-disk weakening during the post-mortem aging of chicken.

Animals↗
PubMed2001

Glucose and palmitic acid induce degeneration of myofibrils and modulate apoptosis in rat adult cardiomyocytes.

Several studies support the concept of a diabetic cardiomyopathy in the absence of discernible coronary artery disease, although its mechanism remains poorly understood. We investigated the role of glucose and palmitic acid on cardiomyocyte apoptosis and on the organization of the contractile apparatus. Exposure of adult rat cardiomyocytes for 18 h to palmitic acid (0.25 and 0.5 mmol/l) resulted in a significant increase of apoptotic cells, whereas increasing glucose concentration to 33.3 mmol/l for up to 8 days had no influence on the apoptosis rate. However, both palmitic acid and elevated glucose concentration alone or in combination had a dramatic destructive effect on the myofibrillar apparatus. The membrane-permeable C2-ceramide but not the metabolically inactive C2-dihydroceramide enhanced apoptosis of cardiomyocytes by 50%, accompanied by detrimental effects on the myofibrils. The palmitic acid-induced effects were impaired by fumonisin B1, an inhibitor of ceramide synthase. Sphingomyelinase, which activates the catabolic pathway of ceramide by metabolizing sphingomyeline to ceramide, did not adversely affect cardiomyocytes. Palmitic acid-induced apoptosis was accompanied by release of cytochrome c from the mitochondria. Aminoguanidine did not prevent glucose-induced myofibrillar degeneration, suggesting that formation of nitric oxide and/or advanced glycation end products play no major role. Taken together, these results suggest that in adult rat cardiac cells, palmitic acid induces apoptosis via de novo ceramide formation and activation of the apoptotic mitochondrial pathway. Conversely, glucose has no influence on adult cardiomyocyte apoptosis. However, both cell nutrients promote degeneration of myofibrils. Thus, gluco- and lipotoxicity may play a central role in the development of diabetic cardiomyopathy.

Animals↗
PubMed2003

Effect of sire on mu- and m-calpain activity and rate of tenderization as indicated by myofibril fragmentation indices of steaks from Brahman cattle.

The objectives of this study were to assess the influence of sire on mu- and m-calpain activities, to evaluate the relationships of activities of these enzymes to other traits related to beef palatability, and to assess the influence of sire on the rate of tenderization (as measured by myofibril fragmentation index [MFI]) in Brahman longissimus muscle. Brahman calves (n = 87), sired by nine bulls, were born, weaned, fed, and slaughtered in central Florida. Traits evaluated were mu- and m-calpain activities and MFI after 1, 7, 14, and 21 d of aging. Other traits were analyzed to determine their associations with mu- and m-calpain activity and MFI, including calpastatin activity, percentage of raw and cooked lipids, Warner-Bratzler shear force (WBSF) values after 7, 14, and 21 d of aging, and sensory panel rating of tenderness, juiciness, and connective tissue amount after 14 d of aging. Data were analyzed using a model with sire, sex, year, and slaughter group (calves of the same sex slaughtered on the same date) as fixed effects, and adjusted to a constant adjusted 12th-rib fat thickness. Sire affected mu-calpain activity (P < 0.04), calpastatin activity (P < 0.01), d-14 MFI (P < 0.02), d-7 WBSF (P < 0.05), d-14 WBSF (P < 0.04), and sensory panel juiciness score (P < 0.01), but not (P < 0.75) m-calpain activity. Measures of tenderness and palatability were generally moderately to strongly correlated (both simple and residual correlations) with calpastatin and m-calpain activity. Myofibril fragmentation index residuals (adjusted for all model components except sire) after all aging periods were fitted using nonlinear regression to the exponential curve (MFI(i) = kappa0 + kappa1 exp[kappa2 t(i)] + epsilon(i), where t(i) represents aging in days, k0 is ultimate MFI after aging, kappa1 is the difference between initial and ultimate MFI, kappa2 is the rate of increase in MFI, and epsilon(i) is the error term associated with the ith observation, assumed to be independent and identically distributed normally). Sires had different estimates and combinations of estimates, which were used to plot MFI change with time. These curves visually differed for sires and suggested that postmortem tenderization extent and rate differ as well. Use of a combination of these estimated parameters in a selection/carcass sorting program represents an alternative consideration for tenderization improvement programs.

Animals↗
PubMed1975

[Protein makeup of rabbit myofibrils determined by a disc eletrophoretic method in the presence of sodium dodecyl sulfate].

The protein subunit composition of isolated myofibrils of rabbit skeletal muscle is studied by polyacrylamide gel disc-electrophoresis in the presense of sodium dodecyl sulfate (SDS). The method of disc-SDS-electrophoresis is described in detail. The electrophoretic patterns of SDS-solubilized myofibrils obtained by disc-SDS-electrophoresis and by SDS-electrophoresis in continuous buffer system according to Weber and Osborn are compared. The former results in a markedly improved resolution and allows to discover some additional protein components, the origin of these additional components being discussed. A standard curve is given for determination of polypeptide chain molecular weights by disc-SDS-electrophoresis.

Animals↗
PubMed2004

Oxidative modification of rat cardiac mitochondrial membranes and myofibrils by hydroxyl radicals.

The effect of hydroxyl radicals generated by the FeSO4/H2O2 system on structural properties of proteins and membranes was studied in rat cardiac mitochondria and myofibrils. Exposure of mitochondria to 0.1 mmol/l FeSO4/EDTA plus 1 mmol/l H202 at 37 degrees C for 30 or 60 min caused conjugated diene formation, but it was not accompanied by accumulation of fluorescent lipid-protein conjugates. On the other hand, fluorescence measurements revealed radical-induced and time-dependent loss of tryptophans and production of bityrosines. Under the same conditions, the gradual decrease in tryptophan flurescence and increase in bityrosine formation was also observed in radical-treated myofibrils. These results suggest that *OH radicals can alter the mitochondrial and myofibrillar function via oxidation of amino acid residues and might be implicated in the pathogenesis of myocardial injury.

Animals↗
PubMed1990

Ca2(+)- and Sr2(+)-sensitivity of the ATPase of myofibrils and natural actomyosins prepared from various muscles.

Ca2(+)- and Sr2(+)-sensitivity of myofibrils and natural actomyosins prepared from various kinds of muscles was investigated by examining the ATPase activity. Sr2+ at concentrations about 30 times higher than Ca2+ was required for activating the ATPase of myofibrils or natural actomyosins from fast skeletal, smooth and scallop striated muscles, while Sr2+ 8-13 times higher than Ca2+ was required for activating the slow skeletal or cardiac system. These findings were consistent with the previous report on the Ca2(+)- and Sr2(+)-sensitive superprecipitation of various natural actomyosins.

Actomyosin↗
PubMed1987

Rotational motions of myosin heads in myofibril studied by phosphorescence anisotropy decay measurements.

We studied the rotational Brownian motions of myosin heads, of which the sulfhydryl group was selectively labeled with the triplet probe 5-eosinylmaleimide, in myofibril by using flash-induced phosphorescence anisotropy decay measurements. The anisotropy decay curve under relaxing conditions consisted of a fast (submicrosecond) and a slow (a few microseconds) component and a small constant part as in the synthetic myosin filaments in solution. The decay curves could be analyzed by assuming that a head part, i.e. subfragment 1 (S1), wobbles in the first cone and a part connecting S1 and the tail of a myosin molecule of which the length is shorter than subfragment 2 (S2) wobbles in the second cone (a double-cone model); the semiangles of the former and the latter cones were about 30 degrees and 50 degrees, respectively. The rotational freedom of myosin heads was only slightly restricted by the limited space of the filament lattice in myofibrils. Under rigor conditions, no motion of myosin heads was observed in the 10-microseconds time scale.

Animals↗
PubMed1989

[Functional state of mitochondria, myofibrils and creatine kinase associated with these organelles of the myocardium in hamsters with hereditary cardiomyopathy].

Functional states of the cardiac contractile apparatus and mitochondria were studied in hamsters with hereditary cardiomyopathy using myocardial fibers with sarcolemma, which had been exposed to saponin. This provided an opportunity of examining the respiratory characteristics of a total mitochondrial population in the myocardium of the animals of two ages (75-100 and 175-200 days). A higher calcium sensitization of myofibrils was found in hamsters with cardiomyopathy. Examination of the rigor tension-MgATP relationship in the presence or absence of phosphocreatine revealed that the animals showed a slightly lower functional activity of myofibrillar creatine kinase. The findings indicate that the creatine kinase system of cardiomyocytes is involved in hereditary cardiomyopathy, mitochondria, in particular, exhibiting much more profound disturbances, in other respects, myofibrils and mitochondria retain their basic functional properties.

Animals↗
PubMed1986

Fast skeletal muscle skinned fibers and myofibrils reconstituted with N-terminal fluorescent analogues of troponin C.

Glycerinated rabbit fast skeletal muscle fibers were chemically skinned with 1% Brij 35 and partially depleted of endogenous troponin C subunit (TnC) by exposure of the fibers to EDTA (Zot, H. G., and Potter, J. D. (1982) J. Biol. Chem. 257, 7678-7683). The TnC-depleted fibers exhibited a decrease in maximal tension that was mostly restored by readdition of TnC or by the addition of the fluorescent 5-dimethylaminonaphthalene-1-sulfonyl aziridine analogue, TnCDanz. TnCDanz is known to undergo an increase in fluorescence intensity when Ca2+ binds to the two low affinity Ca2+-specific regulatory sites of TnC. Steady-state fractional fluorescence and tension changes were measured simultaneously as a function of Ca2+. The Ca2+ sensitivity of the fluorescence curve was about 0.6 log unit greater than the tension curve. This difference in sensitivity could be explained if separate conformational states of TnC, brought about by Ca2+ binding to the Ca2+-specific sites, produce the fluorescence and tension changes. TnC-depleted fibers were also reconstituted with the fluorescent 2-[(4'-iodoacetamido)analino]naphthalene-6-sulfonic acid analogue, cardiac TnCIaans, which undergoes an increase in fluorescence intensity when Ca2+ binds to the single Ca2+- specific regulatory site. The steady-state fractional fluorescence and tension curves for fibers reconstituted with cardiac TnCIaans had nearly the same Ca2+ sensitivity. The steady-state fractional fluorescence of myofibrils reconstituted with TnCDanz was found to have a greater sensitivity to Ca2+ than the simultaneously measured ATPase. In all cases paired fractional fluorescence and activity curves tended to have parallel dependence on Ca2+. These procedures make it possible to study the Ca2+ binding properties of the Ca2+- specific sites in intact myofibrils and skinned fibers; the results presented suggest that the Ca2+ affinity of the Ca2+-specific sites of troponin are reduced in the thin filament compared to that of troponin in solution.

Adenosine Triphosphatases↗
PubMed1987

Differential response of stress fibers and myofibrils to gelsolin.

The actin-severing activity of human platelet gelsolin was analyzed on embryonic skeletal and cardiac myofibrils, and on stress fibers in non-muscle cells. These subcellular structures, although in all three cell types composed of contractile proteins arranged in sarcomeric units, were found to respond differently to gelsolin. The myofibrils in permeabilized myotubes or cardiac cells, as well as in living, microinjected muscle cells proved resistant to a wide concentration range of gelsolin. The same was found for the "mini-sarcomeres" which are seen in developing muscle cells. In contrast, stress fibers in microinjected fibroblasts or epithelial cells, as well as in permeabilized cells, were broken down rapidly by the platelet gelsolin. We conclude from these results that the mini-sarcomeres in embryonic myotubes and cardiac myocytes are not identical with stress fibers.

Actin Cytoskeleton↗
PubMed1988

Myofibril tension fluctuations and molecular mechanisms of contraction.

Recent tension fluctuation experiments that were performed on single myofibrils of cardiac and skeletal muscles established firmly that the fluctuations, if exist, must be below 0.1 ng/square root Hz. This value is about 100 times below the levels that were predicted by various models of cross-bridge mechanical cycling during isometric contraction. Similar measurements with slow stretch and shortening to promote cross-bridge cycling did not produce detectable increase of fluctuations either. Moreover, measurements of elastic transfer function using small length perturbations with white noise clearly demonstrated conduction of vibrations and increased stiffness during contraction of the myofibril; therefore, vibration attenuation within the sarcomere cannot be responsible for remarkable quietness of the tension. Electrostatic mechanism of muscle contraction advanced by Iwazumi gives physically straightforward explanations for the quietness. The ATPase cycling certainly produces fluctuations in the number of surface charges that constitute the dipole moment thus resulting in the field strength fluctuations. However, the magnitude of the fluctuations is only a small fraction of the mean strength due to large number of charges involved in the dipole. In addition, the field strength fluctuations do not couple effectively with the axial force acting on the thin filament bundle. This is due to the combined effects of three factors: 1. Three dimensional three-phase distribution of electrostatic energy density along the thin filament. This structural arrangement smoothes out the forces of three adjacent thin filaments due to complementary nature of the distribution. 2. Characteristic square mesh structure of the Z-disc results in very high shear compliance between adjacent thin filaments yet provides very low parallel compliance. 3. Electrostatic induction.

Animals↗
PubMed1986

The two pathways for oxygen exchange by actomyosin and myofibrils and their dependence on temperature.

At an intermediate stage in the hydrolysis of MgATP by actomyosin there is an exchange of oxygen between water and the terminal phosphoryl group of MgATP, tightly bound to the myosin active site. This intermediate oxygen exchange results from the reversible hydrolysis of the bound MgATP. The rate of the exchange cycle (hydrolysis and the reverse) is assumed to be determined by the rate of reverse hydrolysis; and the average time available for exchange is determined by the post-exchange reaction that immediately follows the cycle. Past analytical studies of the exchange, using actomyosin mixtures and myofibrils at room temperature, have revealed two pathways for hydrolysis, operating at a comparable flux but differing greatly in the extent of exchange they support. It is shown here that these pathways also appear over a range of temperatures from 5 to 30 degrees C and that temperature had little effect on their relative fluxes. At each temperature, the flux ratio (%) for the low exchange pathway: high exchange pathway was near 50:50 for actomyosin mixtures and 60:40 for myofibrils. Apparently, the rate-limiting steps that determine the fluxes of the two pathways have a similar temperature dependence. However, the analysis indicates that one or both of the steps that determine the extent of exchange (reverse-hydrolysis and/or the post-exchange reaction) shows a different temperature dependence for the two pathways. We interpret this to reflect a difference in the temperature dependence of the post-exchange reaction, which we propose is exceedingly fast and independent of actin concentration along the low exchange route, but slow and dependent on the actin concentration along the high exchange route. Thus at all temperatures over a broad range of actin concentration there are two pathways of comparable flux that differ primarily in the time available for exchange.

Actins↗
PubMed1987

[Stress-induced changes in the area ratio or the quantitative ratio of myocardial mitochondria and myofibrils and their correction with thyroid hormones].

An experimental study performed on 30 male white rats has demonstrated that immobilization stress was associated with a decrease in mitochondrial to myofibril area ratio (Smch/Smf) in the left ventricle and interventricular septum by 34.6% and 46.9%, respectively. Pretreatment with small doses of thyroid hormones which did not influence body weight, heart rhythm or serum thyroxin level prevented the decrease and caused Smch/Smf increase in the left ventricle and interventricular septum by 68.7% and 45.8%, respectively. The doses of thyroid hormones applied caused a more marked increase of mitochondrial to myofibril area ratio in the control rats.

Animals↗
PubMed1985

[Effect of phosphate and acidosis on the calcium sensitivity of the cardiac myofibrils].

The treatment of the bundles of rat myocardial fibers with ethyleneglycol-bis(beta-aminoethyl ether)-N,N-tetraacetate (EGTA) made the sarcolemma permeable for ions and small molecules. At the incubation medium pH 7.0 the EGTA-treated fibers developed a half-maximal tension at pCa 5.4, and the maximal tension at pCa 4.8. Inorganic phosphate (10 mM) reduced the maximal tension by 18 +/- 3% and decreased the calcium sensitivity of the myofibrils so that there was a shift of the pCa/tension curve by 0.3 unit to the right. Acidosis (pH 6.6) also decreased significantly the calcium sensitivity, while the presence of 10 mM phosphate produced additional depression of the calcium sensitivity. It is concluded that phosphate accumulation by the ischemic myocardium combined with acidosis may depress the contractility not only due to depletion of the free calcium concentration in the myoplasm but also as a result of the reduced calcium sensitivity of myofibrils.

Acidosis↗
PubMed1979

An electron microscope study of myofibril formation in embryonic rabbit skeletal muscle.

Trunk and limb muscles from fetal and newborn rabbits were investigated by means of light and electron microscopes. At 14 days gestation, the presumptive myoblasts migrate away from the myotome to form the anlage of the muscle of the trunk and limb. Among the population of undifferentiated cells, the myoblasts were recognized due to the presence of actin and myosin filaments. The aggregates of thin and thick filaments appear at the periphery of the cells. There is a great variety of filament assembly. The presence of Z band material appears to be essential for sarcomere formation. At 14 days of gestation the myotubes are more numerous in the limb than in the trunk. The presence of unmaturated fibrils with absence of the M line in the sarcomeres was observed. By day 18 of gestation the myotubes are wider and aggregate to form small bundles. The myofibrils were more numerous and the vesicles of the SR precursor, partly incrustated with ribosomes were dispersed among them. At day 22 of gestation the myotubes are thicker because of the myofibrils which are far more numberous. The sarcomeres were more fully developed, with the M line present. At day 28 of gestation and 3 days after delivery the already developed myofibers were present with a well organized SR system and fully developed sarcomeres.

Animals↗
PubMed1980

[Morphological types of the changes in the myofibrils of cardiac muscle cells].

Light microscopy and electron microscopy examinations showed the changes in myofibrils to be a criterion of early stages of cardiomyocyte involvement. Proceeding from this, the main types of acute cardiomyocyte damage are distinguished: contractures (segmentary and subsegmentary), primary clump degeneration, intracellular myocytolysis and cytolysis. The best way to detect the state of myofibrils by light microscopy is to use polarization microscopy which diagnoses in sections acute metabolic damages and early stages of myocardial infarction, repeated and relapsing infarctions, fibrillation of ventricles. The utilization of polarization microscopy in pathological practice permits one to diagnose definitely the early stages of acute damages of the heart in cases of sudden and unexpected death.

Animals↗
PubMed1977

Tension generation by isolated myofibrils.

The technique for mechanical dissection of microscopic myofibrilar bundles containing few myofibrils is described. A sensitive electrooptical tension transducer capable of resolving the tension generated by such myofibrilar bundles to within a fraction of a percent is used to study the response of the preparations to low ATP concentrations. The rate of tension development decreased with a decrease in ATP concentration. Below 10(-6) M ATP the myofibrils did not demonstrate any mechanical activity at all. These findings are discussed in terms of the kinetics of the cross-bridge cycle.

Adenosine Triphosphate↗
PubMed1995

[Quantitative light and electron microscopy studies of myofibrils and mitochondria of dog and chicken hearts].

Ventricular myocytes are characterized by a central nucleus which is surrounded by longitudinal myofibrils and a mostly column-like longitudinal distribution of mitochondria. This study was designed to investigate the subcellular distribution of organelles in close proximity to the nucleus. Of particular interest was the question of whether volume density of organelles close to the nucleus is maintained and, as a consequence, if the cellular diameter at the site of the nucleus is increased according to the dimension of the nucleus. Therefore, dog and chicken hearts were subjected to perfusion fixation and sections of myocytes were studied in longitudinal and cross-sectional axes by light and electron microscopy. Volume density of organelles was analyzed on longitudinal sections according to Rosiwal's principle and on cross-sections by the point-counting method and a digitalized imaging system. We found that the cross-sectional diameter of cardiac myocytes is slightly wider at the site of the nucleus according to the dimension of the nucleus. The volume density of myofibrils and mitochondria is similar in most subcellular fractions except at the nuclear poles where mitochondria were significantly more abundant. Thus, no significant disturbance of the organelle distribution is observed at the site of the nucleus.

Animals↗