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PubMed1992

Effect of porcine stress syndrome on the solubility and degradation of myofibrillar/cytoskeletal proteins.

This study examined the effect of stress classification (stress-positive, stress-carrier, stress-negative) of pigs on selected properties of postmortem muscle, including protein solubility and degradation of proteins such as titin. Longissimus muscle samples were removed 45 min postslaughter, divided into samples, and stored at 0 to 2 degrees C for analysis at 0, 1, 3, 5, and 7 d postmortem. Whole-muscle samples (homogenates) and purified myofibrils were prepared from each sample for analysis by SDS-PAGE. A portion of each muscle sample also was extracted 1) with a low-ionic-strength solution to obtain a sarcoplasmic protein fraction and 2) with two different high-ionic-strength solutions to obtain a myofibrillar/cytoskeletal protein fraction for measurement of protein solubility and for analysis of extracts by SDS-PAGE. No significant differences were observed between muscle from stress-negative and stress-carrier animals in this study. Sarcoplasmic (P less than .05) and myofibrillar/cytoskeletal (P less than .01) protein solubility was lower in muscle samples from stress-positive animals than in muscle samples from stress-carrier and stress-negative animals at all postmortem times studied. The high molecular weight protein titin was degraded more slowly postmortem in muscle from stress-positive than in muscle from stress-negative animals, as observed by SDS-PAGE analysis of whole-muscle samples (homogenates) an myofibrils. The combination of lowered protein solubility and reduced rate of postmortem degradation of structural proteins such as titin may explain, at least in part, the reduced quality and protein functionality of muscle from stress-positive pigs.

Animals↗
PubMed1997

Effect of rapid rigor mortis processes on protein functionality in pectoralis major muscle of domestic turkeys.

The pale, soft, exudative (PSE) phenomenon in turkey pectoralis major (breast) muscle was studied using a combination of biochemical, meat quality, microscopic, and gel electrophoresis techniques. Breast muscle samples were collected from turkeys characterized by slow vs fast postmortem glycolysis assessed by muscle pH at 20 min after death. The PSE group was characterized by lower muscle ATP (P < .05) and higher lactate levels (P < .05) compared with the normal group. Excess water-holding capacity and cooking yield were significantly lower (P < .05) in the PSE group than in normal turkeys. Breast muscle of the PSE group was also lighter (P < .05) than that in the normal group as determined by Minolta L* values. The SDS-PAGE, Western blotting, and immunofluorescence microscopy revealed that phosphorylase, a soluble enzyme, became tightly associated with the myofibrils in muscle from the PSE group. Also, less myosin could be solubilized from PSE vs normal myofibril samples. The results indicate that irreversible myosin insolubility due to low pH and high-temperature conditions is decisive in the development of PSE turkey breast muscle.

Adenosine Triphosphate↗
PubMed2006

Dephosphorylation specificities of protein phosphatase for cardiac troponin I, troponin T, and sites within troponin T.

Protein dephosphorylation by protein phosphatase 1 (PP1), acting in concert with protein kinase C (PKC) and protein kinase A (PKA), is a pivotal regulatory mechanism of protein phosphorylation. Isolated rat cardiac myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 were used in determining dephosphorylation specificities, Ca(2+)-stimulated Mg(2+)ATPase activities, and Ca(2+) sensitivities. In reconstituted troponin (Tn) complex, PP1 displayed distinct substrate specificity in dephosphorylation of TnT preferentially to TnI, in vitro. In situ phosphorylation of cardiomyocytes with calyculin A, a protein phosphatase inhibitor, resulted in an increase in the phosphorylation stiochiometry of TnT (0.3 to 0.5 (67%)), TnI (2.6 to 3.6 (38%)), and MLC2 (0.4 to 1.7 (325%)). These results further confirmed that though MLC2 is the preferred target substrate for protein phosphatase in the thick filament, the Tn complex (TnI and TnT) from thin filament and C-protein in the thick filament are also protein phosphatase substrates. Our in vitro dephosphorylation experiments revealed that while PP1 differentially dephosphorylated within TnT at multiple sites, TnI was uniformly dephosphorylated. Phosphopeptide maps from the in vitro experiments show that TnT phosphopeptides at spots 4A and 4B are much more resistant to PP1 dephosphorylation than other TnT phosphopeptides. Mg(2+)ATPase assays of myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 delineated that while PKC and PKA phosphorylation decreased the Ca(2+)-stimulated Mg(2+)ATPase activities, dephosphorylation antagonistically restored it. PKC and PKA phosphorylation decreased Ca(2+) sensitivity to 3.6 microM and 5.0 microM respectively. However, dephosphorylation restored the Mg(2+)ATPase activity of PKC (99%) and PKA (95%), along with the Ca(2+) sensitivities (3.3 microM and 3.0 microM, respectively).

Animals↗
PubMed1976

[Molecular mechanisms of cardiac insufficiency in myocardial ischemia].

An analysis of the main concepts of the pathogenesis of heart muscle insufficiency under ischaemia was conducted. None of the hypotheses postulating the invariability of the energy supply to the myofibrills was shown to explain the fast reduction of the contractility of the ischaemic myocardium. These hypotheses are based on the experimental fact of the ATP level in the myocardium practically undergoing no reduction under ischaemia. At the same time, one of the earliest changes in the heart muscle under ichaemia consists in creatine phosphate concentration reduction that correlates with the decrease in the contractility. The recently obtained data indicate that the energy synthesized in the mitochondria of the cardiac muscle is carried away from them in the form of energy of creatine phosphate molecules that is later used for ATP synthesis in the myofibrill creatine phosphokinase reaction. A scheme is suggested that implies that under ischaemia severe changes in the energy supply consisting in creatine phosphate synthesis reduction are the leading factor in the pathogenesis resulting on the early stages of the process in a reduction of the contractility, and on the later ones--in irreversible damages of the membrane systems and cell destruction.

Adenosine Triphosphate↗
PubMed1975

Alterations in energy metabolism and ultrastructure upon reperfusion of the ischemic myocardium after coronary occlusion.

The effects on myocardial function, metabolism and ultrastructure of 60 minutes of reperfusion, instituted after 30, 60 and 90 minutes of occlusion of the left anterior descending coronary artery, were studied in 48 dogs. Twelve sham-operated dogs served as controls. Coronary occlusion for 60 or 90 minutes caused significant depression in the first derivative of left ventricular pressure (dP/dt) (P less than 0.05) that could not be reversed by reperfusion. Upon reperfusion, creatine phosphate stores in myocardium made ischemic for 30 and 60 minutes, but not for 90 minutes, returned toward control levels, but stores of adenosine triphosphate (ATP) and total nucleotides and the ATP/adenosine diphosphate ratio of myocardium subjected to 60 and 90 minutes of ischemia were further decreased. After 60 and 90 minutes of ischemia, swelling of the sarcoplasmic reticulum and mitochondrial damage (swelling, decreased matrix density and partial loss of cristae) were seen. Myofibrils were relaxed in all these groups. Reperfusion produced gross contraction of myofibrils and aggravated these changes in mitochondria and sarcoplasmic reticulum. In the hearts subjected to 90 minutes of ischemia these changes were gross. The levels of creatine phosphokinase, glutamic oxaloacetic transaminase and lactic dehydrogenase in the coronary sinus blood increased dramatically (P less than 0.05) upon reperfusion after 60 or 90 minutes of occlusion, indicating severe impairment of cell membranes. This secondary rise in serum enzyme activity during reperfusion should be taken into consideration when estimating the size of a myocardial infarct from enzyme changes alone. It appears that 60 and 90 minutes of ischemia cause severe myocardial damage that is not reversed by reperfusion maintained for 1 hour although longer periods of reperfusion may be beneficial.

Animals↗
PubMed1979

Chicken parvalbumin. Comparison with parvalbumin-like protein and three other components (Mr = 8,000 to 13,000).

Procedures for a rapid isolation and purification of parvalbumin (Mr = 12,600), parvalbumin-like protein (Mr = 12,800), and three other polypeptides with molecular weights of 12,400 (Component 1), 11,700 (Component 2), and 8,000, respectively, from chicken leg muscle, are described. A direct comparison of parvalbumin with these other proteins showed distinct differences in the amino acid compositions, charge, and immunological behavior. Parvalbumin has two high affinity sites for Ca2+ with a KDiss less than or equal to 10(-6) M (Blum, H. E., Lehky, P., Kohler, L., Stein, E.A., and Fischer, E. H. (1977) J. Biol. Chem. 252, 2834-2838), in contrast to parvalbumin-like protein. Components 1 and 2, and the Mr = 8,000 protein, where only low affinity sites for Ca2+ could be detected (KDiss greater than 10(-3) M). From our results it is concluded that the co-extracted proteins do not constitute isoproteins of parvalbumin. The very low affinity for Ca2+ suggests that these proteins are not involved in processes of Ca2+ transport or Ca2+ regulation as proposed for parvalbumin. Parvalbumin could not be localized within isolated myofibrils and also did not accumulate in primary myogenic cell cultures together with proteins forming the myofibrillar structure. Parvalbumin was not even detected in myotubes in which myofibrils and sarcoplasmatic reticulum were already assembled and functioning. Parvalbumin (or cross-reacting material) was detected in leg muscle and brain 1 day after hatching of the chick. Possible roles for parvalbumin are discussed.

Aging↗
PubMed2001

Ultrastructural distribution of the S100A1 Ca2+-binding protein in the human heart.

Impaired calcium homeostasis and altered expression of Ca2+-binding proteins are associated with cardiomyopathies, myocardial hypertrophy, infarction or ischemia. S100A1 protein with its modulatory effect on different target proteins has been proposed as one of potential candidates which could participate in these pathological processes. The exact localization of S100A1 in human heart cells on the ultrastructural level accompanied with biochemical determination of its target proteins may help clarify the role of S100A1 in heart muscle. In the present study the distribution of the S100A1 protein using postembedding (Lowicryl K4M) immunocytochemical method in human heart muscle has been determined quantitatively, relating number of antigen sites to the unit area of a respective structural component. S100A1 antigen sites have been detected in elements of sarcoplasmic reticulum (SR), in myofibrils at all levels of sarcomere and in mitochondria, the density of immunolabeling at Z-lines being about 3 times and at SR more than 5 times higher than immunolabeling of remaining structural components. The presence of the S100A1 in SR and myofibrils may be related to the known target proteins for S100A1 at these sites.

Adult↗
PubMed1975

Structure and innervation of extraocular muscles of Carassius.

The extraocular muscles of the carp Carassius contain two types of muscle fibre. Large white fibres have ribbon-shaped peripheral myofibrils and triads located at the Z line. Small red fibres, rich in mitochondria, have polygonal-shaped myofibrils and triads at the A-I junction. Silver- and cholinesterase-stained preparations show that the large fibres are innervated by axons which spiral around them and exhibit intense cholinesterase activity over long distances. Axons supplying small muscle fibres run across bundles of fibres, making one contact with each fibre. By electron microscopy the nerve endings on each fibre type appear identical, both having a smooth post-junctional muscle membrane. The differences in structure and innervation pattern of the two fibre types are discussed in relation to their possible functional roles.

Animals↗
PubMed1975

[Ultrastructure of the cellular elements of mouse rhabdomyosarcoma].

The ultrastructure of different types of cell elements of rhabdomyosarcoma clones induced by 20-methylcholanthrene in mice CC57W is described. Along with general signs of a decreased differentiation typical for blastic cells of different histogenesis (rough endoplasmic reticulum, an abundance of free ribosomes, etc) some types of cell elements of myoblasts are characterized by specific features such as the character of anastomoses, fibrillary structures, etc. Morover, as a pathognomonic sign for tumorous myoblasts at the ultrastructural level could be only the presence of myofibrils with periodic aggragations like Z-bands in their cytoplasm. Since within one clone population both cells with and without myofibrils were encountered, the absence of the latter should not be considered to be a criterion for denying the myogenic nature of such cell elements.

Animals↗
PubMed1975

[Effect of allergic damage on plastic metabolism of the myocardium in rabbits].

The plastic metabolism of the myocardium in rabbits was studied after varying periods of allergic damage induced by repeated injections of normal horse serum. An accelerated decompostion of the myofibril proteins was demomstrated to occur during the acute phase. During the reparation phase, an activation of the protein synthesis in the myocardium occurred. The newly synthesized myofibril proteins had a longer turnover in the tissues, than under normal conditions. The turnover time of the mitochondrial proteins did not differ from the normal one.

Acid Phosphatase↗
PubMed1975

The inhibitory action of the light meromyosin component on the myofibrillar and actomyosin atp-ase.

The protein component of light meromyosin [LMM-1] was shown earlier to relax glycerinated muscle fibres and actomyosin. Presently its influence on ATP-ase activity of myofibrils, actomyosin, myosin and heavy meromyosin has been studied. LMM-1 decreases Mg-ATP-ase activity of myofibrils and of reconstructed actomyosin by 25-- 30% and does not change [or slightly increases] Ca-ATP-ase activity of this protein and of myosin; besides LMM-1 is able to increase Mg-ATP-ase of HMM substantially. LMM-1 markedly inhibits [preliminary data] the activation of ATP-ase activity of HMM by actin. It is suggested that LMM-1 protein interacts with myosin and decreases the actin-myosin affinity, displacing actin out of the complex. It reacts only with one of the heads of myosin. Probably this suggestion can account for a relatively slight inhibition of ATP-ase activity of complex by LMM-1. LMM-1 represents a natural and specific inhibitor of Mg-AM-ATP-ase activity, included in the structure of myosin protofibrils and interacting with the myosin active site region.

Actins↗
PubMed1975

Ultrastructure of the contractile system of striated skeletal muscle and the processes of muscular contraction. II. Releasing system and mechanisms of muscular contraction.

The tropomyosin-troponin system of the thin filaments acts as a regulator of the interaction of myosin with actin by a process of inhibition. This inhibition is released by Ca2+ ions. Muscle contraction occurs when Ca+2 ions are released from the sarcoplasmic reticulum into the myofibril, where they interact with the troponin of the thin filaments. Muscular contraction is due to the sliding of the two kinds of filaments past each other in the hexagonal network of the myofibril. Many hypotheses have been formulated concerning the intimate molecular mechanisms responsible for the sliding of the filaments past each other, but none of these can be considered to be entirely satisfactory.

Actins↗
PubMed1976

Dependence of calcium release, tension generation and restoring forces on sarcomere length in skinned cardiac cells.

The ascending limb of the length-tension diagram was studied in single skinned (sarcolemma-free) cardiac cells of rat ventricle. The free (Ca2+) in the perfusing solutions was buffered with ethyleneglycol-bis(beta-aminoethyl)N,N'-tetraacetic acid (EGTA). Tension was recorded with a photo-diode force transducer (detection limit: 1 mug, compliance 2-3 mum/mg) and was expressed as a function of the sarcomere length (SL) measured during contraction with a high-speed movie camera. When the SL was decreased by a brief (1-2 sec) exposure to high free (Ca2+), a restoring force qas observed upon return of the cell to a relaxing solution. The restoring force was comprised of two components: (1) a rapid elongation to 1.57 identical to 0.06 mum developing a negative tension (relaxing force) as large as 4% of the maximum positive tension, which was observed in both skinned cells and in single myofibrils, and (2) a slow elongation from 1.57 identical to 0.06 to 1.93 identical to 0.14 mum, which was observed in skinned cells but not in single myofibrils. When the SL was kept extremely short by continuous Ca2+ activation for more than 30 sec, a shortening of the A band much below 1.0 mum persisted for several minutes after imposed re-elongation of the sarcomers (delta state). The amplitude of the tonic tension developed by direct activation of the myofilaments in the presence of high total (EGTA) was maximum for 2.20 mum SL and decreased very little when the SL was decreased. However, the decrease of tension became more pronounced at SL shorter than 1.55 mum when polyvinylpyrrolidone was added to the solutions at a concentration reducing the swelling of the myofilament lattice. This finding imposes some caution in applying the results obtained in skinned cardiac cells to intact tissue. The SL-tension diagram of the phasic contractions induced by Ca2+-triggered of Ca2+ in the presence of a slight EGTA buffering was similar to the SL-tension diagram of the intact rat ventricular muscle when the latter was expressed as a function of the active SL. In contrast, the SL-tension diagram of caffeine-induced phasic contractions was similar to that of the tonic tension produced by direct activation of the myofilaments. Decreasing SL results therefore in a partial inhibition of the Ca2+ triggered release process. It was concluded that Starling's Law may correspond to a length-dependence of several mechanisms including Ca2+-triggered release from the SR, interaction between thick and thin filaments and restoring forces.

Calcium↗
PubMed1975

'Immobile' (im), a recessive lethal mutation of Xenopus laevis tadpoles.

'Immobile' (im) is a recessive lethal mutation discovered in the F3 of a Xenopus (Xenopus laevis laevis) originating from a mesodermal nucleus of a neurula transplanted into an enucleated egg. The im embryos do not contract after mechanical stimulation nor do they present any spontaneous contraction from the neurula stage onwards. Development proceeds normally during the first days after which deformation of the lower jaw and tail are observed. The im tadpoles die when normal controls are at the feeding stage. Nevous and muscular tissues are histologically normal in the mutant tadpoles; at advanced stages, however, an irregularity in the path of the myofibrils is observed which is especially conspicuous in the electron microscope. Cholinesterases and ATPase are present in the mutant muscles. Parabiosis and chimerae experiments have shown that parabionts and grafts behave according to their own genotype. Cultures of presumptive axial systems with or without ectoderm lead to the conclusion that, first of all, the abnormality is situated in the mesodermal cells and secondly that the first muscular contractions in normal Xenopus laevis are of myogenic origin. The banding pattern of the myofibrils is normal as was shown by obtaining contractions of glycerol extracted in myoblasts with ATP. It seems therefore that in this mutation, the abnormality is situated in the membraneous system of the muscular cell, sarcoplasmic reticulum and/or tubular system as is probably the case in the mdg mutation of the mouse.

Adenosine Triphosphatases↗
PubMed1975

The spectrum of degenerative changes in hypertrophied human cardiac muscle cells: an ultrastructural study.

Light and electron microscopic observations were made on cardiac tissues removed at operation from 91 patients with ventricular hypertrophy, including left ventricular myocardium from 16 patients with aortic valvular disease and from 16 patients with asymmetric septal hypertrophy, and crista supraventricularis muscle from 59 patients with congenital heart diseases associated with right ventricular outflow tract obstruction. In all patients the majority of cardiac muscle cells were hypertrophied, had intact myofibrils, and were surrounded by small amounts of fibrous tissue. In 18 (20%) of the 91 patients cardiac muscle cells with a wide spectrum of degenerative changes were present in addition to hyperthrophied, nondegenerated cells. Early degenerative changes consisted of focal myofibrillar lysis, with preferential loss of thick myofilaments, and focal proliferation of tubules of sarcoplasmic reticulum. Cardiac muscle cells with advanced degeneration had extensive myofibrillar damage and a marked decrease in numbers of myofibrils and T-tubules. The most severely degenerated cells showed selective proliferation of organelles, including sarcoplasmic reticulum, mitochondria, and glycogen, which replaced the contractile elements in the cytoplasm. These findings suggest that degenerated cardiac muscle cells have poor contractile function and may be responsible for impaired cardiac performance in some patients with ventricular hypertrophy. These morphological features appear to represent a final common pathway for degeneration of cardiac muscle cells in a variety of cardiac conditions.

Aortic Valve Insufficiency↗
PubMed1992

[Lesions of ventricular cardiomyocytes in experimental massive pulmonary embolism].

The damage of ventricular myocardial cells during acute experimental massive pulmonary embolism (MPE) was studied by light, polarization and electron microscopy on anaesthetized dogs. In cases, when MPE was followed by heart failure, the deep ir reversible damage of myofibrils took place, and the relative volume of myofibrils decreased in both ventricles. The damage of right ventricular myocardium, which works against increased postload during MPE, may be reason of right ventricular insufficiency.

Animals↗
PubMed1979

Changes in the contractile material of human skeletal muscle following tendinous injury.

The most marked changes in the human muscle following tendinous injury can be observed in the contractile components. There is a widening of the Z-membrane, dispersion of the sarcomers, a break in their continuity, and detached bundles of myofibrils are found in the sarcoplasm. A change occurs also in the proportion of different fibre types of the muscles, in the muscle with tendinous injury a predominance of type II fibre becoming apparent. Among the proteins of myofibrils a product of disintegration of a molecular weight of 31 000 can be consequently demonstrated, and in some muscles products of disintegration with a molecular weight between 90 000 and 58,000 arise.

Adenosine Triphosphatases↗
PubMed1991

Morphometric study of ventricular myocardial cells in the bat (Pipistrellus pipistrellus), hamster (Mesocricetus auratus) and Wistar rat.

A comparative morphometric study of ventricular myocardial cells of the West African insect-eating the Pipistrellus pipistrellus, the hamster and the rat revealed significant differences in volume fractions of mitochondria myofibrils, lipid bodies and T tubules. In the cells of the bat, mitochondria constitute 35% of cytoplasmic volume compared with 29 and 30% in the hamster and rat, respectively. Notably, crista density is much higher in the bat cells (3.58 x 10(5) cm-1) than in those of the hamster (2.59 x 10(5) cm-1) and of the rat (2.48 x 10(5) cm-1). Myofibril concentration is 40% in the bat, 53% in the hamster and 55% in the rat. There is greater numerical density of lipid bodies in the bat (212.27 x 10(9) cm-3) than in the hamster (139.20 x 10(9) cm-3) and in the rat (114.00 x 10(9) cm-3). The volume occupied by T tubules is 0.02 in the bat and hamster, and 0.009 in the rat. These differences suggest structural design for efficient metabolic activity in the bat which, among mammals, has high exercise tolerance.

Adaptation, Physiological↗