Arrangement Of Myofibrils Research Articles

Synthetic strands of neonatal mouse cardiac myocytes: structural and electrophysiological properties.

The aim of the present study was to morphologically and electrically characterize synthetic strands of mouse ventricular myocytes. Linear strands of mouse ventricular myocytes with widths of 34.7+/-4.4 microm (W(1)), 57.9+/-2.5 microm (W(2)), and 86.4+/-3. 6 microm (W(3)) and a length of 10 mm were produced on glass coverslips with a photolithographic technique. Action potentials (APs) were measured from individual cells within the strands with cell-attached microelectrodes. Impulse propagation and AP upstrokes were measured with multisite optical mapping (RH237). Immunostaining was performed to assess cell-cell connections and myofibril arrangement with polyclonal antisera against connexin43 and N-cadherins and monoclonal antibodies against cardiac myosin. Light microscopy and myosin staining showed dense growth of well-developed elongated myocytes with lengths of 34.2+/-4.2 microm (W(1)), 36. 9+/-5.8 microm (W(2)), and 43.7+/-6.9 microm (W(3)), and length/width ratios of 3.9+/-0.2. Gap junctions were distributed around the cell borders (3 to 4 junctions/microm(2) cell area). Each cell was connected by gap junctions to 6.5+/-1.1 neighboring cells. AP duration shortened with time in culture (action potential duration at 50% repolarization: day 4, 103+/-34 ms; day 8, 16+/-3 ms; P:<0.01). Minimum diastolic potential and AP amplitude were 71+/-5 and 97.2+/-7.6 mV, respectively. Conduction velocity and the maximum dV/dt of the AP upstroke were 43.9+/-13.6 cm/s and 196+/-67 V/s, respectively. Thus, neonatal ventricular mouse myocytes can be grown in continuous synthetic strands. Gap junction distribution is similar to the neonatal pattern observed in the hearts of larger mammals. Conduction velocity is in the range observed in adult mice and in the higher range for mammalian species probably due to the higher dV/dt(max). This technique will permit the study of propagation, AP, and structure-function relations at cellular resolution in genetically modified mice.

Elevated Activity of Cathepsin L-like Protease in the Jellied Meat of Japanese Flounder.

The cause of the jelification of Japanese flounder meat was investigated. Infection by parasites was not histologically detected, while the arrangement of myofibrils was notably disturbed. Large amounts of trichloroacetic acid soluble materials and a breakdown of myosin heavy chain suggested the occurrence of proteolytic degradation in the jellied meat.Crude extract of the jellied meat showed proteolytic activity on myosin heavy chain, which was hardly detected in the normal meat. The extract hydrolyzed Z-Phe-Arg-MCA most preferentially among the synthetic peptide substrates tested. Activities on myosin heavy chain and Z-Phe-Arg-MCA were inhibited by leupeptin, antipain, and E-64, but not by soybean trypsin inhibitor or pAPMSF (a specific inhibitor for trypsin-like proteases), suggesting that the activities were ascribed to a cysteine protease(s). Both myosin heavy chain and Z-Phe-Arg-MCA hydrolyzing activities were co-eluted from TSK G3000SWXL column at an eluting position whose molecular weight corresponded to 34, 000. Together with these results, the protease activity elevated and possibly involved in the jelification of Japanese flounder meat was taken to be due to an endogenous cathepsin L-like protease.

Mode of action of rabbit skeletal muscle cathepsin B towards myofibrillar proteins and the myofibrillar structure

1. 1. The mode of degradation of myofibrillar proteins and the structural changes in myofibrils due to the action of cathepsin B highly purified from rabbit skeletal muscle were studied. 2. 2. Cathepsin B degraded myosin heavy chain, actin and troponin T, but not α-actinin, tropomyosin, troponin I or troponin C among myofibrillar proteins. 3. 3. Cathepsin B optimally degraded myosin heavy chain, actin and troponin T at around pH 5. Degradation of myosin heavy chain produced 6 fragments, 180,000, 150,000, 87,000, 81,000, 75,000 and 69,000 Da, respectively. Actin was hydrolyzed into fragments of 41,000, 38,000 and 30,000 Da. Troponin T was degraded into fragments of 21,000, 12,000 and 10,000 Da. 4. 4. Cathepsin B caused the fragmentation of myofibrils and disturbance of the lateral arrangement of myofibrils. 5. 5. Cathepsin B partly disintegrated the Z-line and the M-line, and induced disordering of the arrangement of filaments in the I-band.

The pattern of organization of intermediate filaments and their asymmetrical association with dense bodies in smooth muscle of an ascidian Halocynthia roretzi

An extensive network of intermediate filaments that interconnected cytoplasmic dense bodies and connected the dense bodies to the cell surface was revealed in double-fixed, tannic acid-stained preparations of ascidian smooth muscle. The filament network ran through spaces in the continuous network of myofibrils, connecting them longitudinally, obliquely and transversely to form an intimately associated, dual network. In their transverse passage, the intermediate filaments ran across myofibrils along I-zones exclusively, interconnecting successive dense bodies. The pattern of attachment of intermediate filaments to dense bodies was predominantly “one-sided.” The filaments, which themselves were not incorporated into the contractile apparatus, remained folded or unfolded between myofibrils and between sarcomere-like structures in synchrony with the contraction-relaxation cycles. These results suggest that the intermediate filaments mechanically maintain the organization and arrangement of myofibrils via an intimate association with the myofibrils in the regions of the dense bodies, in such a way that the filaments do not impede muscle function. Based on these observations, a new model for the network of intermediate filaments in smooth muscle cells is proposed.

Cultured heart cells from the spontaneously diabetic KK mouse.

In order to clarify the mechanism of myocardial changes in KK mice, cultured heart cells from both normal and spontaneously diabetic KK mice were studied by electron microscopy, photoelectric recording, and 45Ca activity. Compared with cultured heart cells from normal mice, those from KK mice showed a decrease in beating frequency and ceased beating more rapidly. The rhythm of the beating cells from KK mice became irregular, while that of the heart cells from normal mice was not changed significantly over a period of 10 days. Electron micrographs of cultured heart cells from KK mice showed an increased number of mitochondria, an intricate arrangement of myofibrils, poorly formed Z bands, and a lipidlike substance. The 45Ca activity of heart cells from KK mice, after incubation for 24 h in a medium containing 45Ca, was increased compared with heart cells from normal mice. Based on these findings, we conclude that ultrastructural alterations exist in cultured heart cells from KK mice and we suggest that an increase of intracellular Ca might play an important role in the pathogenesis.

Histologic and ultrastructural studies on the myocardium in spontaneously diabetic KK mice: A new animal model of cardiomyopathy

The hearts from spontaneously diabetic KK mice and control mice were examined by light and electron microscopy. Myocardial degeneration, myocardial fibrosis and calcium deposits in the myocardium were extensive in KK mice aged 8 weeks. In myocytes of newborn KK mice, an irregular arrangement of myofibrils and poorly formed Z bands were found. Ultrastructural changes in myocytes of KK mice aged 4 weeks consisted of destruction of mitochondria, degenerated myofibrils and abnormalities of Z bands. However, increased mucopolysaccharides in interstitium and thickened basement membranes of capillaries were not found in KK mice, in contrast to the previous reports of myocardial changes in diabetic C57BL/KsJ mice, alloxan-diabetic dogs and hypertensive-diabetic rats. These observations suggest that the cardiomyopathy found in KK mice is not secondary to diabetes mellitus but is caused by other factors. In conclusion, myocardial ultrastructural abnormalities are present in newborn KK mice. Thus, this animal can be used as a model of cardiomyopathy.

Morphological changes in myofibrils and glycerinated muscle fibers on treatment with cathepsins d and L

1. 1. Morphological changes in myofibrils and glycerinated muscle fibers on treatment with cathepsins D and L obtained from rabbit skeletal muscle were studied by phase contrast and electron microscopy. 2. 2. Cathepsin D degraded the Z-line and filaments adjacent to the H-zone. 3. 3. Cathepsin L caused the fragmentation of myofibrils, and degraded the Z-line and M-line. 4. 4. Both cathepsins induced disturbance of the lateral arrangement of myofibrils.

A peculiar myofibrillar pattern in the murine muscle-tendon junction.

The muscle-tendon junctions of adult mice show a special arrangement of myofibrils. Essentially, the myofibrils are oriented in an anchor-like manner in the large finger-shaped processes of the muscle fiber, which contain "mitochondrial sacks" (Demmel et al. 1979) in a subsarcolemmal position. Furthermore, the single myofibril frequently branches out into smaller fibrils. It is suggested that due to the three-dimensional arrangement, these processes gain a high rigidity during contraction, thus maintaining their shape and preserving the "mitochondrial sacks".

In situ reconstitution of myosin filaments within the myosin-extracted myofibril in cultured skeletal muscle cells.

We studied the in situ reconstitution of myosin filaments within the myosin-extracted myofibrils in cultured chick embryo skeletal muscle cells using the electron microscope and polarization microscope. Myosin was first extracted from the myofibrils in glycerinated muscle cells with a high-salt solution containing 0.6 M KCl. When rabbit skeletal muscle myosin was added to the myosin-extracted cells in the high-salt solution, thin filaments in the ghost myofibrils were bound with myosin to form arrowhead complexes. Subsequent dilution of KCl in the myosin solution to 0.1 M resulted in the formation of thick myosin filaments within the myofibrils, increasing the birefringence of the myofibrils. When Mg-ATP was added such myosin-reassembled myofibrils were induced either to form supercontraction bands or to restore the sarcomeric arrangement of thick and thin filaments. Under the polarization microscope, vibrational movement of the myofibrils was seen transiently upon addition of Mg-ATP, often resulting in a regular arrangement of myofibrils in register. These myofibrils, with reconstituted myosin filaments, structurally and functionally resembled the native myofibrils. The findings are discussed with special reference to the myofibril formation in developing muscle cells.

An electron microscopic study on the extraocular muscles of a lamprey, Lampetra japonica.

This paper reports an EM study on the observations of the extraocular muscles of the lamprey, Lampetra japonica. Individual muscles consisted of numerous subunits, each being surrounded by a common external lamina and containing two, S- and F-types, of muscle fibers. A subunit contained an average of 8.25 muscle fibers consisting of 5.58 S-type fibers and 2.67 F-type fibers. In a rectus anterior muscle, the total number of the S-type fiber was 852, the average cross-sectional area being 144 micrometer 2. The total number of the F-type fiber was 397, the average cross-sectional area being 300 micrometer 2. The S-type fiber was characterized by the arrangement of myofibrils as a single layer in the cortical sarcoplasm as well as by the development of peripheral couplings. The F-type fiber was characterized by the presence of central myofibrils in the juxtanuclear sarcoplasm in addition to peripheral myofibrils and by the development of the T-system and triads at the level of the Z line. M lines appeared distinct in the F-type fibers and less distinct in the S-type fibers. Muscle fibers within individual subunits were separated from each other by a space about 20 nm, but no membrane specializations such as gap junction or desmosome have been determined to exist between adjacent muscle fibers.

Electron microscopic study of cardiac lesions induced in rats by isoproterenol and by repeated stress. With suggestion that idiopathic cardiomyopathy may be a "disease of adaptation".

An electron microscopic study of cardiac lesions induced in rats by isoproterenol and by repeated stress is described, and a possible pathogenetic mechanism of idiopathic cardiomyopathy is proposed. Three types of cardiac cells could be roughly differentiated according to the structure and arrangement of myofibrils: 1) normo-type with normal structure and normal arrangement of myofibrils, 2) nondestroyed-degenerated-type in which myofibrils show normal structure and abnormal arrangement, and 3) destroyed-degenerated-type with destroyed myofibrils. Various degrees and frequency of mitochondrial changes (accumulation, variation of size, swelling, loss of cristae and myelin figure), increase of glycogen granules, dilation of sarcoplasmic reticulum or T-tubules and nuclear changes were seen in every type. These 3 types seemed to correlate well with the degree of myocardial beta-adrenergic stimulation by isoproterenol or repeated stress. Normo-types were extensively observed in hearts exposed to mild myocardial beta-adrenergic stimulation. Nondestroyed-degenerated-types and destroyed-degenerated-types were frequently observed in hearts exposed to excessive myocardial beta-adrenergic stimulation. These results show a similarity between cardiac lesions induced in rats by isoproterenol or repeated stress and those seen in human idiopathic cardiomyopathy, and suggest the possibility that idiopathic cardiomyopathy is a "Disease of Adaptation."

Cardiomyocytes in the embryonal stage of syrian hamsters with a hereditary cardiomyopathy

Comparative studies were made histologically and ultrastructurally of the hearts of embryos of an inbred strain of Syrian hamster (B10 14.6) having a hereditary idiopathic cardiomyopathy, and of an unrelated healthy hamster (BIO RB). The incidence of immature cardiomyoblasts was higher in the cardiomyopathic hamsters than in the controls. A disturbance of the myofibril formation was seen in the hearts of diseased embryonic hamsters despite the accelerated ribosomal synthesis and increased number of mitosis. This disturbance appears to be related to the development of the postnatal heart lesions in this strain. With regard to the etiology of cardiomyopathy, possible intervention of unknown factors which could impede the proper arrangement of myofibrils from their building-blocks should be considered. Neurosecretory granules were found in the vicinity of the nucleus of ventricular cardiomyocytes of the cardiomyopathic embryonic hamsters. To clarify the significance of these granules, further study is necessary.

Electron Microscopic Study of Extraocular Muscles in Myotonic Dystrophy

The extraocular muscles of two middle-aged men with ophthalmoplegia secondary to myotonic dystrophy were studied by electron microscopy. The main change was disorganization in the arrangement of myofibrils rather than degeneration of the cells. Diseased muscle cells contained randomly distributed, short and irregular myofibrils and individual myofilaments. The cytologic appearance of these muscle cells was similar to that of developing muscle cells. The pathogenesis of the myopathy in myotonic dystrophy may be related to myofibrillogenesis and its maintenance.