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PubMed1976

Ultrastructural changes in hypertrophied myocardium of spontaneously hypertensive rats.

In seven arbitrarily selected groups of 3-, 5-, 9-, 11-, 15-, and 21-week and one-year-old spontaneously hypertensive rats (SHR) (F25-26), qualitative as well as quantitative light and electron microscope studies were conducted on the myocardium in the left ventricular papillary muscle and lateral wall. Age-and body-weight-matched groups of normotensive Wistar-Kyoto rats were employed as controls. In the strain of SHR used in this study blood pressure was significantly higher than in the controls in the 7th week of age, reached sustained levels (approximately 180 mmHg) in the 15th week of age and remained higher thereafter. The heart weight/body weight ratio gradually increased in SHR after the 15th week of age. In 3-week-old SHR, there was no significant difference in fine structure of the myocardium in comparison with control animals. The cardiocytes were small in size and rapidly growing. Myofibrillogenesis seemed to occur in association with juvenile forms of intercalated discs, subsarcolemmal dense mats, occasional Z band expansions and unorganized filamentous structures in the periphery of preexisting myofibrils. In 5- and 9-week-old SHR, the muscle fiber diameters in the papillary muscle were significantly larger than those in control animals of the same age. Subcellular structures of many cardiocytes were, however, apparently equal in both papillary muscle and lateral wall of the left ventricle in SHR and control animals. In 11-week-old SHR, the cardiocytes were moderately hypertrophied in both papillary muscle and lateral wall. The myofibrils were significantly increased in mass in association with altered intercalated discs, extended subsarcolemmal dense mats and unorganized filamentous structures in the periphery of preexisting myofibrils. Focal interstitial fibroses occurred in in the myocardium, and tunnel capillaries appeared in some hypertrophied cardiocytes. In 15-week-old SHR, the cardiocytes had markedly hypertrophied in accordance with the establishment of sustained hypertension. The intracellular volume ratios of myofibrils and T system had increased significantly whereas the mitochondrial volume had markedly decreased resulting in a significant increase in the myofibril/mitochondria volume ratio. There were marked changes in the intercalated discs associated with numerous immature sarcomers, and frequent abnormal Z band expansions. Interstitial fibroses had markedly increased in number and extent. In 21-week-old SHR, in addition to findings similar to those in 15-week-old SHR, heterogeneous changes of the contractile material, mitochondria and sarcoplasmic matrix were more prominent, suggesting heterogeneous malfunctions in later stages of cardiac hypertrophy. In one-year-old SHR, subcellular changes in many cardiocytes qualitatively resembled those in 21-week-old SHR. Interstitial fibroses and tunnel capillaries were also increased in extent and number...

Age Factors↗
PubMed1979

Intracellular distribution of calcium in cardiac muscles studied by electron microscope autoradiography.

The intracellular distribution of calcium was investigated by 45Ca electron microscope autoradiography in the frog or rat ventricular muscle and guinea pig papillary muscle. The muscle was incubated for 30 min in 45Ca-Ringer's solution or high Ca solution in which 1/10--1/20 of Ca was replaced with 45Ca. The distribution of developed silver grains sensitized by the 45Ca (45Ca grains) was found to be 38% in the mitochondria, 43% in the myofibrils and 19% in the other regions (8% in the cytoplasma and 11% in the various membranous structures) in the frog muscle cell incubated in the 45Ca-Ringer's solution. After electrical stimulation (10 Hz, 5 min), the distribution was 22% in the mitochondria, 53% in the myofibrils and 25% in other regions. Similar results were obtained after high K stimulation in the frog ventricular muscles and after electrical stimulation in high Ca solution in guinea pig papillary muscles. Following the addition of 1 X 10(-6) g/ml adrenaline into the incubating solution, the grain distribution in guinea pig papillary muscles did not show significant change but the distribution in myofibril decreased after electrical stimulation, while it increased in the mitochondria. Longitudinal localization of 45Ca grains along the myofibril was also examined and it was a general tendency throughout all animals examined that the grain density at the A band and near the Z band decreased after electrical stimulation, while it increased at the I band and, especially, at the A-I junction.

Animals↗
PubMed1987

Ionic strength and myofibrillar protein solubilization.

Myofibrils from bovine longissimus muscle were obtained at 2 h postmortem and incubated in .10 to .35 M ionic strength buffers under various conditions in vitro. Increasing ionic strength or increasing the incubation time from 1 to 72 h decreased the turbidity of suspensions of myofibrils and increased myofibrillar solubilization (P less than .01 for both measures). The use of KCl or NaCl to elevate ionic strength gave essentially identical results, but lactate generally was ineffective in changing either the percentage myofibrillar solubilization or the turbidity of suspensions of myofibrils. Gel electrophoresis under denaturing conditions indicated that KCl was more effective than NaCl in causing the release of C-protein from myofibrils, and both salts were quite effective in dissociating M-protein, actin, troponin-T, tropomyosin, myosin light chain-3 and a 30,000-dalton molecular weight protein from myofilaments. Small increases in alpha-actinin also were observed, especially in samples incubated for 72 h. Substantially more myosin light chain-3, tropomyosin (or paratropomyosin) and troponin-T, and less actin and the 30,000-dalton protein, were released in samples incubated at pH 5.5 than at pH 7.0 (P less than .05). Electron micrographs indicated loss of thick filament ultrastructure after incubation for 24 h in either .1 or .3 M ionic strength, but the Z-lines were largely unaffected. In samples that had first been incubated with trypsin for 10 min, the Z-lines were virtually indistinguishable at .1 M ionic strength, and absolutely no myofibrillar structures could be discerned in samples incubated in .3 M ionic strength buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Myofibrillar Ca2+-stimulated Mg2+-ATPase from chronically ischemic canine heart.

Functional properties of myofibrils from chronically ischemic canine myocardium were evaluated. Ischemia was produced by tight stenosis of left anterior descending artery (LAD), followed by 40 min acute ischemia with prior preconditioning. Animals of the first group were sacrificed after 8 weeks. In the second group, angioplasty of LAD was performed after 8 weeks of ischemia and animals were kept alive for other 4 weeks. Control animals were sham operated. Activity and kinetic parameters of myofibrillar Ca2+-stimulated Mg2+-ATPase were measured in myofibrils isolated from anterior and posterior parts of all hearts. We did not find any differences in maximal velocity (Vmax), half-maximal activation constant for calcium (K(Ca2+)50) and cooperativity coefficient (n(hill)) of myofibrils from different experimental groups as compared to controls, either at pH 7, pH 6.5 (acidosis) or pH 7.5 (alkalosis). K(Ca2+)50 increased in medium simulated acidosis (12.6-33.5 times) and n(hill) decreased significantly in all groups as compared with values obtained at pH 7. These results indicate that activity and Ca2+-sensitivity of myofibrillar Mg2+-ATPase remain unchanged despite deteriorated heart function 8 weeks after LAD obstruction. Experiments have confirmed that Ca2+-stimulated-ATPase from canine heart myofibrils responded to pH decrease by a decreased sensitivity to Ca2+ and a decreased cooperativity. However, sensitivity of the enzyme to the pH changes is unaltered by 8 weeks of chronic ischemia.

Angioplasty, Balloon, Coronary↗
PubMed1991

Studies of the alpha-actinin/actin interaction in the Z-disk by using calpain.

Both mu- and m-calpain (the micro- and millimolar Ca(2+)-requiring Ca(2+)-dependent proteinases) can completely remove Z-disks from skeletal muscle myofibrils and leave a space devoid of filaments in the Z-disk area. alpha-Actinin, a principal protein component of Z-disks, is removed from myofibrils by the calpains, and a 100-kDa polypeptide that comigrates in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the alpha-actinin subunit is released into the supernatant. Purified calpain does not degrade purified actin or purified alpha-actinin as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by N- and C-terminal amino acid analysis of calpain-treated and untreated alpha-actinin and actin. The 100-kDa polypeptide released from myofibrils by calpain elutes identically with native alpha-actinin off DEAE-cellulose and hydroxyapatite columns and, after purification, binds to pure F-actin in the same manner that untreated, native alpha-actinin binds. Calpain-released alpha-actinin also accelerates the rate of superprecipitation of reconstituted actomyosin, a sensitive property characteristic of native alpha-actinin. Consequently, the calpains release alpha-actinin from the Z-disk of myofibrils without degrading it or without altering its ability to bind to actin. These results indicate that alpha-actinin does not simply cross-link thin filaments across the Z-disk but that at least one additional protein (or perhaps an altered actin or alpha-actinin) is involved in the alpha-actinin/actin interaction in Z-disks.

Actinin↗
PubMed1985

Actin filaments and acetylcholine receptor clusters in embryonic chick myotubes.

The tumor-promoting drug 4 beta-phorbol 12-myristate 13-acetate (TPA) causes the loss of myofibrils in primary cultures of chick embryonic myotubes [9]. When myofibrils in chick myotubes are dispersed by TPA treatment (5 X 10(-8) M), there remains a class of non-myofibrillar actin filaments that are sensitive to subsequent breakdown by cytochalasin D. Microfilament bundles in fibroblasts in the same cultures seem unaffected by this TPA treatment, but are also broken down by cytochalasin D (0.2 micrograms/ml); this dose has little effect on myofibrils. We have previously shown that treatment of chick myotubes with cytochalasins would destabilize clusters of acetylcholine receptors (AChRs) [6]. In order to further examine the relationship between actin filaments and cell surface AChRs, we have used the receptor-specific ligand alpha bungarotoxin (a-BGT) to study the fate of AChR clusters in drug-treated and control myotubes. Cells treated with TPA showed no loss in the number of receptor clusters present on their surface. However, if these cells were also treated with cytochalasin D, cluster number was reduced to approximately the same value as seen for cytochalasin treatment alone (50% of the control value). These results suggest that the cytoskeletal link to these cell surface receptors is not mediated by attachment to the alpha actin-containing myofibrils, but rather clustered AChRs are stabilized by a class of non-myofibrillar actin filaments.

Actins↗
PubMed1989

[Changes in alpha-actinin localization and myofibrillogenesis in rat cardiomyocytes under cultivation].

By indirect immunofluorescence with monoclonal anti-alpha-actinin antibodies the localization of this contractile protein was studied in ventricular cardiac myocytes from newborn 2-4-day old rats in the course of their cultivation. In freshly isolated heart muscle cells a predominant longitudinal orientation of myofibrils was observed; in some cells on the periphery of cytoplasm the contours of Z-lines are indistinct. During cell spreading, in the areas of intercalated discs, growing processes were observed mostly containing no contractile structures at earlier stages of cultivation. On days 3 to 14, the cytoplasmic processes and ruffles are filled with developing myofibrils. The cultures are heterogeneous in the morphology of contractile apparatus of individual cells. In most cardiomyocytes mature myofibrils are well-developed in the central part of the cytoplasm, whereas in its peripheral areas non-myofibrillar stress-fiber-like structures and bundles with continuous distribution of alpha-actinin frequently connected to myofibrils are more typical. In the areas of active myofibrillogenesis, located mainly on the cell periphery, numerous alpha-actinin dots are observed; most of them are arranged linearly and periodically at a distance of 0.3-1.5 microns and seem to be structural precursors of Z-lines. The data obtained show that the cultures of mammalian cardiac cells may be a convenient object for studying myofibrillogenesis in the course of cardiomyogenic differentiation.

Actinin↗
PubMed1984

The effect of acidic pH on the ATPase activity and troponin Ca2+ binding of rabbit skeletal myofilaments.

We compared the effect of reductions in pH from 7.0 to 6.5 and to 6.2 on Mg-ATPase activity and Ca2+ binding of rabbit psoas myofilaments. The amounts of Ca2+ bound attributable to myofilament whole troponin complexes (Tn) were determined from studies on Tn free (desensitized) myofibrils and from measurements of the myofilament Ca2+ binding subunit of Tn content (0.55 +/- 0.10 nmol/mg of myofilament protein). The myofibrillar Mg-ATPase activity was half-maximal at the -log molar free Ca2+ concentration (pCa) 5.83 at pH 7.0, 5.54 at pH 6.5, and 5.43 at pH 6.2 Maximal ATPase activity was the same at the three pH values as was the ATPase activity of desensitized myofibrils. The amounts of Ca2+ bound to myofibrils or chemically skinned fibers as a function of pCa decreased as pH was lowered from 7.0 to 6.5 and to 6.2 in a manner predicted from the pH-induced shifts in Mg-ATPase activity as a function of pCa. The alterations in myofibrillar ATPase activity and Ca2+ binding associated with the acidic pH values occurred whether or not EGTA was used to buffer the free Ca2+ concentration. Moreover, lowering the pH from 7.0 to 6.2 reduced Ca2+ binding to myofilament Tn whether or not the fibers and myofibrils were in rigor. Our data indicate that the effects of acidic pH on myofilament ATPase activity and Ca2+-binding are related to a reduction in the affinity of Ca2+-binding sites on Tn.

Adenosine Triphosphatases↗
PubMed1981

Effects of isoproterenol treatment of isolated perfused rat hearts on myofibrillar phosphorylation and ATPase activity.

Perfusion of isolated rat hearts with isoproterenol resulted in increases in the level of protein-bound phosphate of the myofibrils. After perfusion of the hearts with 32P, followed by SDS-polyacrylamide gel electrophoresis of the purified myofibrils, four major 32P-containing protein bands were identified. Most of the increased 32P incorporation produced by isoproterenol was localized on the troponin I and myosin light chain bands, and, to lesser extent, on the M-protein band. ATPase activity was tested in the purified myofibrils. No changes in Ca2+ requirement for activation were found after isoproterenol perfusion. However, maximal ATPase activity was markedly reduced in the myofibrils obtained from isoproterenol-treated hearts. It would appear that the myofibrillar protein phosphorylation induced by isoproterenol perfusion results in a decrease in actomyosin ATPase activity.

Animals↗
PubMed1980

Immunofluorescence studies for myosin, alpha-actinin and tropomyosin in developing hearts of normal and cardiac lethal mutant Mexican axolotls, Ambystoma mexicanum.

Recessive mutant gene c in axolotl embryos results in an absence of normal heart function. Immunofluorescence studies were done to determine the distributions of myosin, tropomyosin and alpha-actinin in the hearts of normal and mutant siblings. Anti-myosin specifically stains the A bands of myofibrils in normal hearts and reveals a progressive increase in myofibril organization with development. Mutant hearts display less staining for myosin than normal and localization is mainly in amorphous collections. Anti-alpha-actinin stains the Z lines of myofibrils in normal myocytes. Mutant cells also have significant staining for alpha-actinin but show no striations. Antitropomyosin intensely stains the I bands of myofibrils in normal cells; however, there is very little staining for tropomyosin in mutant hearts. Thus, mutant myocardial cells have reduced but significant amounts of actin (Lemanski, Mooseker, Peachey & Iyengar, 1976) and myosin, even though non-filamentous, and substantial amounts of alpha-actinin. The cells appear to contain little tropomyosin.

Actinin↗
PubMed1982

Differentiation of fibre types in an extraocular muscle of the rat.

Mammalian extraocular muscles possess greater variation in structural and physiological properties than any other muscle. The superior rectus muscle of the adult rat contains five morphological fibre types. The differentiation of the muscle into these fibre types in embryonic and postnatal rats were studied by light and electron microscopy, and the distribution of each developing fibre type with its distinctive features was mapped. The muscle of the 18-day embryos did not display the specific structural fibre types that were observed in the adult muscle. Newborn rat muscle exhibited some differentiation that included scattered small-diameter fibres with large myofibrils (fibre type 'B'). As development proceeded, another small-diameter fibre type with small myofibrils (fibre type 'A') appeared in the 6-day postnatal rat muscle. By the end of the first week of development neuromuscular junctions were in evidence in these two fibre types. Postsynaptic folds were rare in the large-fibril fibre, and folds were extensive in the small-fibril fibre. The medium- (fibre type 'C') and large-diameter (fibre type 'D') fibres were fully differentiated with small myofibrils and abundant sarcoplasmic reticulum (SR) by the second week of the development. SR was most abundant in the large-diameter fibre, which constituted the predominant global fibre type in the adult muscle. The postsynaptic folds in the neuromuscular junctions of these two fibre types were highly developed, although the innervation did not extend widely in the global region of the muscle. The last fibre type (fibre type 'E') was fully differentiated with the largest myofibrils, a small amount of SR, and simple neuromuscular junction by the third week of the postnatal development. The superior rectus muscle of the four-week-old rat was differentiated with all fibre types present in the adult muscle. During the third to sixth, and final, week of development, the other types described above exhibited extensive differentiation of characteristic structural features.

Animals↗
PubMed1981

[Quantitative ultrastructural findings of the myocardium in the failing heart. I. Aortic valve insufficiency (author's transl)].

Quantitative ultrastructural changes of the left ventricular (LV) myocardium and contractile function were studied in 9 symptomatic patients with severe aortic insufficiency (AI). The volume fractions of myofibrils, sarcoplasm, and mitochondria in myocardial cells were determined by electron microscopic morphometry in small LV tissue samples. Interstitial fibrosis was measured by light microscopic morphometry. Transmural biopsies of the LV free wall perfused by the left anterior descending coronary artery (LAD) were obtained during aortic valve replacement. Biopsies from the LAD-perfusion area of 10 surgical patients with coronary artery disease but moderate LAD-stenosis and normal regional motion of LAD-area were taken as controls for morphometric data. LV-function was analyzed from preoperative heart catheterization. In initial reproducibility studies of biopsy samples of 17 patients a sampling error for evaluation of myocardium was defined and differences exceeding 6.2% transmural fibrosis and 6.5% myofibrils were considered biologically significant differences. Patients with AI had higher LV end-diastolic volume (180 versus 77 ml/m2, p less than 0.001), and lower LV ejection fraction (51 versus 69%, p less than 0.001) than 10 control individuals. The volume fraction of myofibrils was lower in AI than in controls (44 versus 53%, p less than 0.01), and sarcoplasm was higher (33 versus 21%, p less than 0.01). Mitochondria and interstitial fibrosis did not differ between groups (p greater than 0.05). Thus reduction in the volume fraction of myofibrils was the major ultrastructural finding in LV biopsy samples of patients with heart failure due to aortic insufficiency.

Adult↗
PubMed1993

Comparison of postmortem autolysis in cardiac and skeletal muscle.

To understand the mechanism in postmortem autolysis better, processes in the postmortem degradation of myofibril proteins in the presence of protease inhibitors were studied. Male Wistar rats were given injections of the carboxyl-, thiol-, and serine-protease inhibitors, pepstatin, Ep-475[L-transepoxysuccinyl-leucylamide(3-methyl) butane; E-64-C], and chymostatin, via the femoral vein. Control rats were similarly treated with saline. Then, myofibril proteins were isolated from their cardiac and femoral muscles and from those of control animals at various times after death, and degradation of these myofibril proteins with time was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In cardiac muscle, alpha-actinin was degraded rapidly, followed by the heavy chain of myosin and light chain of myosin (L2). Actin and the light chain of myosin (L1) were degraded slowly. the degradations of the heavy chain of myosin, alpha-actinin, tropomyosin and L2 after 14 days were not inhibited by pepstatin, but were inhibited by Ep-475 and chymostatin. In skeletal muscle, L1 and L2 were degraded rapidly, followed by the heavy chain of myosin and alpha-actinin. Actin was degraded slowly and was still unchanged 2 weeks after death. The degradations of protein components were inhibited by pepstatin, Ep-475 and chymostatin. These results indicated that after death the components of myofibrils are degraded by various proteases at various rates depending on their properties or structures. This degradation is fundamentally the same in cardiac and skeletal muscles, but inhibitors have somewhat different effects on the postmortem degradation processes after death in the two types of muscle.

Animals↗
PubMed1993

Ultrastructural changes of myotendinous junctions in tenotomized soleus muscles of the rat.

The effects of tenotomy on the ultrastructure of myotendinous junctions in the rat soleus muscle were studied by thin-section electron microscopy. When the soleus muscle was tenotomized at both distal and proximal ends, virtually all muscle fibers showed a characteristic alteration called central core lesion in their middle portions. The similar alteration was also found in the end portions of each muscle fiber. As early as 5 days after tenotomy, myofibrils at the fiber end were extensively disoriented and disintegrated with thickening of the Z-discs. The surface specializations, sarcoplasmic processes and invaginations of the fiber end were also altered in such a way that the sarcoplasmic processes retracted. The disintegration of myofibrils was most extensive at one week after tenotomy, often losing their association with the sarcolemma. The thickening and rod formation of the Z-discs at the fiber ends were prominent at 1 and 2 weeks. The thickened Z-discs and rod structures were never closely associated with the sarcolemmal undercoats, which were not significantly thickened. This suggests that the Z-disc and the sarcolemmal undercoat are discrete entities. Interestingly, the basal laminae were frequently seen to be separated from the sarcolemma forming free sheets, as the sarcoplasmic processes retracted. In the space surrounded by such free basal lamina were seen many vesicular or granular materials. At 3 and 4 weeks the fiber end showed a recovery process forming new myofibrils, as the sarcoplasmic processes grew long. Thus, the surface specializations of the fiber end were much more elaborate than those in the control muscle. At 5 and 6 weeks the myotendinous junctions returned to normal ultrastructure except that the surface specializations were still elaborated. These findings demonstrated that the myotendinous junction underwent a series of characteristic alterations and recovery of the surface specializations as well as myofibrils.

Animals↗
PubMed1993

[Histopathology and ultrastructural changes of the musculature and nerves during methamidophos toxication in chicken].

After exposure to methamidophos (Via digestive or respiratory tract or just by skin contamination) for 1, 2, 3, 4, 8 and 12 weeks respectively, ultrastructure of the myofibrils in chicken with methamidophos toxication via the digestive tract showed mild degeneration in the first week and serious degeneration by the end of the fourth week. Light microscopy of the muscle-fibril showed atrophy and necrosis in the third week, including both myopathic atrophy and neuropathic atrophy. Recovery of the lesions took place from the 8th to the 12th week (Light or elcetion microscopy). Those chickenstaking immunosuppressive drug simultaneously with methamidophos exposure (via digestive tract) showed less degeneration of the myofibrils and nerves. Ultrastructure of the myofibril in chickens with methamidophos intoxication through the respiratory tract also developed less degeneration of myofibrils and nerves than those obtained through digestive intoxication. There was no lesion obtained in chicken taking methamidophos via the respiratory tract coexistently with the immunosuppressive drug or just by skin contamination.

Animals↗
PubMed1976

[Fibrillary structures in tumor myoblasts].

An electron microscope study was made of fibrillar structures in various types of cell elements in mice rhabdomyosarcoma. Different stages of myofibril development were followed in such differentiated cell elements as large spindle cells, large round cells and middle spindle cells. In the former two cells, the evolution has riched a stage of bundles of myofibrills with Z-like bands. The highest degree of myofibril maturation occurs in multinuclear myosymplasts. The occurrence of myofibrils being at different stages of evolution within the same cells is characteristic of tumor myoblasts in addition to an excentric unipolarity of cell differentiation and atypical structure of Z-brands. Cytotypical differentiation (myofibrillogenesis in uninuclear cells) may be the case only in those types of rhabdomyosarcoma cell elements which are able to undergo histottypical differentiation (fussion and formation of multinuclear myosymplasts).

Animals↗
PubMed1996

Living adult rat cardiomyocytes in culture: evidence for dissociation of costameric distribution of vinculin from costameric distributions of attachments.

Adult rat cardiomyocytes were placed in tissue culture to determine the relationships of their vinculin positive costameres, their attachments associated with the costameres, the fate of their myofibrils. The costameric structures were detected using interference contrast microscopy and the visualization of the fluorescently labeled vinculin and alpha-actinin molecules. The cardiomyocytes isolated from the heart retained their myofibrils upon attachment to the cell surfaces. One group of cells then rounded up, only to respread after 6 days in culture. These cells initially demonstrated costameric distributions of attachments and vinculin. These relationships were lost during the rounding-up process only to be regained as the cells respread. The second group of freshly isolated cardiomyocytes did not round up but began to spread on the substratum by sending out lamellipodia from their rectangularly shaped body. These newly cultured cardiomyocytes initially exhibited costameric distributions of close attachments detected by interference microscopy. Over the next 3 days although the cells remain attached to the substratum, the costameric attachments were gradually lost. Nevertheless, when similar cells were injected with fluorescently labeled vinculin, costameric distributions of vinculin could be detected in the absence of costameric attachments. Cardiomyocytes, injected with fluorescent alpha-actinin, revealed that during the first few days in culture the existing myofibrils disassembled from the edges of the cell towards the middle. The center group of myofibrils was retained as the cells began to spread. Our observations of living cells support the hypothesis that proteins in addition to vinculin are needed for cardiomyocytes to generate costameric attachments to the cell surfaces. We speculate that the ability of the vinculin-attached Z-lines of adult cardiomyocytes to dissociate from the extracellular matrix may aid in the remodeling of the adult heart in the repair process after myocardial infarction and also in stress induced hypertrophic growth.

Actins↗
PubMed1997

Embryonic, juvenile, and adult development of the toadfish sonic muscle.

BACKGROUND: Sonic muscle fibers intrinsic to the swim bladder of the oyster toadfish Opsanus tau proliferate throughout adult life and have an unusual radial morphology: alternating ribbons of sarcoplasmic reticulum (SR) and myofibrils surround a central core of sarcoplasm. Large fibers in adults form multiple cores, fragment, and appear to divide into smaller, more energy efficient units. METHODS: We examined embryonic to adult development of sonic muscle using electron and light microscopy and focused on the incidence of satellite cells (SC). RESULTS: Muscle fibers form late in the larval period from myoblasts, which do not appear to fuse into myotubes, but enlarge and differentiate myofibrils in a single patch. The SR differentiates from the outside inward, separating the myofibrils into bundles of varying thickness, which often exceed the thickness seen in adults. SCs in juveniles and adults have a sparse cytoplasm and a heterochromatic nucleus. The % SC nuclei (SC nuclei/total nuclei) decreases from a high of 88% in larvae to a low of 1% in adults although the adult average is 10%. No embryonic type fibers in the process of differentiating myofibrils were seen in adults. Small immature fibers, which had not yet formed the central core, have a complete radially organized contractile cylinder. CONCLUSIONS: Immature muscle fibers formed embryonically in the larval period have a different morphology from immature fibers in adults, suggesting that splitting rather than SCs is a major source of new fibers in adults.

Air Sacs↗