Biomedical subjects

K Trombitás

Publications and source records attributed to K Trombitás.

At least 19 recordsLinked to original sources

PubMed1995

[Mitochondrial DNA deletion in hereditary cardio-encephalo-myopathy].

The case of a female patient with cardio-encephalo-myopathy who died of her illness at one year of age, similarly to her three sisters, is reported. In autopsy samples, like muscle, heart, liver and cerebellum activities of several mitochondrial enzymes were determined. In the skeletal muscle serious decrease of carnitine acetyltransferase was observed (from the normal 4.8 U/g to 0.08 U/g wet weight), while in other tissues this activity was normal. In the muscle activities of several other mitochondrial enzymes were also decreased (cytochrome oxidase, NADH cytochrome C oxidoreductase, citrate synthase), while in other tissues there were no similar changes. Serious distortion was observed in the structure of the majority of mitochondria of muscle and heart by electronmicroscopy. The number of the Purkinje-cells in the cerebellum decreased, and the cells were shrunken, their axons were fragmented and disoriented. Also the structure of the mitochondria was abnormal in the Purkinje-cells, while it was normal in other areas of the cerebrum. In te tissues of the patient normal and deleted mitochondrial DNA coexisted as which could explain the genetic background of this disease at molecular level.

Autopsy↗

PubMed1995

The mechanically active domain of titin in cardiac muscle.

One of the main contributors to passive tension of the myocardium is titin. However, it is not exactly known what portions of this approximately 1 micron-long molecule are anchored in the sarcomere (hence, are rendered inelastic) and what portions are elastic (hence, are mechanically active in developing passive tension). We assessed the length of the elastic domain of cardiac titin by ultrastructural and mechanical methods. Single cardiac myocytes were stretched by various amounts, and while in the stretched state, they were processed for immunoelectron microscopy. Several monoclonal anti-titin antibodies were used, and the locations of the titin epitopes in the sarcomere were studied as a function of sarcomere length. Only a small fraction (5% to 10%) of the approximately 1000-nm-long molecule behaved elastically under physiological conditions. This mechanically active domain is located close to the A/I junction, and its contour length when unstretched is estimated at approximately 50 to 100 nm. In sarcomeres that are slack (length approximately 1.85 microns), the mechanically active domain is folded on top of itself, and the length of the domain reaches an elastic limit of approximately 550 nm in sarcomeres that are approximately 2.9 microns long.

Animals↗

PubMed1993

Shortening-induced tension enhancement: implication for length-tension relations.

Length-tension relations come in two types--the classical type with linearly descending limb, and the "flat," higher type. The classical type, now confirmed in several laboratories, is obtained when sarcomeres are servo-controlled to maintain constant length. The flat type, also confirmed in several laboratories, is obtained in fixed-end contractions, where some sarcomeres have the opportunity to shorten at least slightly. We find that the higher tensions seen in the flat type are indeed the result of very small shortening: when isometric sarcomeres shorten to a slightly shorter (e.g., by 40 nm) length, they go on to produce considerably more isometric tension than if they had remained at the shorter length throughout contraction. We term this phenomenon "shortening-induced tension enhancement." The phenomenon accounts not only for the higher, flatter length-tension relation seen in fixed-end contractions but can explain the creep of tension that occurs in extended tetani. Thus, several issues concerning the interpretation of length-tension relations are resolved by this newly discovered phenomenon.

Animals↗

PubMed1993

Elastic properties of connecting filaments along the sarcomere.

The elasticity of the connecting filament--the filament that anchors the thick filament to the Z-line--has been investigated using rigor release, freeze-break and immunolabelling techniques. When relaxed insect flight muscle was stretched and then allowed to go into rigor, then released, the recoil forces of the connecting filaments caused sarcomeres to shorten. Thin filaments, prevented from sliding by rigor links, were found crumpled against the Z-line. Thus, rigor release experiments demonstrate the spring-like nature of the connecting filaments in insect flight muscle. In vertebrate skeletal muscle, however, the same protocol did not result in sarcomere shortening. Absence of shortening was due to either smaller stiffness of connecting filaments and/or higher stiffness of the thin filaments relative to insect flight muscle. The spring-like nature of the connecting filament was confirmed with the freeze break technique. When the frozen sarcomeres were broken along the A-I junction, the broken connecting filaments retracted to the N1-line level, independently of the thin filaments, demonstrating the basic elastic nature of these filaments. To study the elastic properties of the connecting filaments along the sarcomere, the muscle was labelled with monoclonal antibodies against a titin epitope near the N1-line, and another very near the A-I junction in the I-band. Before labelling, fibers were pre-stretched to varying extents.(ABSTRACT TRUNCATED AT 250 WORDS)

Actin Cytoskeleton↗

PubMed1993

Elastic properties of the titin filament in the Z-line region of vertebrate striated muscle.

The characteristics of the titin filament in the vicinity of the Z-line were investigated using immunoelectron microscopy. We used monoclonal titin antibodies T-11 and T-12 on single fibres of frog skeletal muscle, and on Z-line-extracted fibres. It is well established that the I-band region of titin is elastic. We find, however, that the elastic properties are not uniform. The T-12 epitope, which binds near the Z-line at the N1-line level, hardly changes position relative to the Z-line as the sarcomere is stretched. This demonstrates the functional inextensibility of the N1-Z-line region. After extreme stretch (above 6-microns sarcomere length), this zone finally does elongate; thus, the titin molecule in this region is intrinsically elastic. The functional inextensibility seen at shorter sarcomere lengths may, therefore, be a result of binding of titin to the actin filament in the zone near the Z-line. When the Z-line was extracted, the T-12 epitope remained in the same position as in the unextracted fibres; it did not retract from the Z-line. Failure to retract implies that functional anchoring of titin is not exclusive to the Z-line, but includes some site closer to the A-band. Combined with the results of the above-mentioned stretch experiment, this result implies a likely binding of titin to the thin filament either focally at the N1 line or all along the entire N1-Z region. Thus, this region of titin is functionally stiff, but intrinsically elastic.

Animals↗

PubMed1993

Contraction-induced movements of water in single fibres of frog skeletal muscle.

Although X-ray diffraction measurements imply almost constant filament separation during isometric contraction, such constancy does not hold at the level of the isolated cell; cell cross-section increases substantially during isometric contraction. This expansion could arise from accumulation of water drawn from other fibre regions, or from water drawn into the cell from outside. To distinguish between these hypotheses, we froze single fibres of frog skeletal muscle that were jacketed by a thin layer of water. Frozen fibres were freeze-substituted, sectioned transversely, and examined in the electron microscope. In fibres frozen during contraction, we found large amounts of water just beneath the sarcolemma, less in deeper regions, and almost none in the fibre core. Such gradients were absent or diminished in fibres frozen in the relaxed state. The water was not confined to the myofibril space alone; we found large water spaces between myofibrils, particularly near mitochondria. Accumulation of water between myofibrils and around mitochondria implies that the driving force for water movement probably lies outside the filament lattice, and may therefore be osmotic. The fact that the distribution was nonuniform-highest near the sarcolemma and lowest in the core--implies that the water was likely drawn from the thin jacket surrounding the cell. Thus, the contractile cycle appears to be associated with water entry into and exit from the cell.

Animals↗

PubMed1993

[Questions concerning two-stage reconstruction of injured flexor tendons. III. Ultrastructure of the tenosynovium in the pseudo-tendon sheath created by using a silicone rod].

Authors have investigated the ultrastructure of the pseudo tendon sheath, formed with silicon rod and man. They have observed a superficial structure, resembling the normal tendon sheath in scanning electron microscopic examination. With transmission electron microscopy phagocyte "A" type and secretion "B" type synovial cells were found. Authors state that the newly formed tenosynovium has an important role in the nutrition of the tendon graft and the prevention of adhesions.

Animals↗

PubMed1991

Nature and origin of gap filaments in striated muscle.

Immunoelectron microscopy was used to study the nature and origin of 'gap' filaments in frog semitendinosus muscle. Gap filaments are fine longitudinal filaments observable only in sarcomeres stretched beyond thick/thin filament overlap: they occupy the gap between the tips of thick and thin filaments. To test whether the gap filaments are part of the titin-filament system, we employed monoclonal antibodies to titin (T-11, Sigma) and observed the location of the epitope at a series of sarcomere lengths. At resting sarcomere length, the epitope was positioned in the I-band approximately 50 nm beyond the apparent ends of the thick filament. The location did not change perceptibly with increasing sarcomere length up to 3.6 microns. Above 3.6 microns, the span between the epitope and the end of the A-band abruptly increased, and above 4 microns, the antibodies could be seen to decorate the gap filaments. Between 5 and 6 microns, the epitope remained approximately in the middle of the gap. Even with this high degree of stretch, the label remained more or less aligned across the myofibril. The abrupt increase of span beyond 3.6 microns implies that the A-band domain of titin is pulled free of its anchor points along the thick filament, and moves toward the gap. Although this domain is functionally inextensible at physiological sarcomere length, the epitope movement in extremely stretched muscle shows that it is intrinsically elastic. Thus, the evidence confirms that gap filaments are clearly part of the titin-filament system. They are derived not only from the I-band domain of titin, but also from its A-band domain.

Animals↗

PubMed1991

Results of ultrastructural analysis of the calf muscles in clubfoot.

Open biopsies were carried out on the muscles of 23 clubfoot patients, ages 9 months to 4 years. Electron microscopic analyses of the so-called "clubfoot muscles" and the peroneal muscles were performed. The changes found were not present in every area of the muscles, but were surrounded by fields of normal structure. Fatty degeneration with fibrosis was observed as the consequence of immobilization. More marked loss was found in the contractile elements. The authors believe that neuromuscular atrophy is a primary cause of congenital clubfoot. The most seriously affected muscles in this study were the tibialis posterior and peroneal muscles. The material failed to prove correlation with age. Based on their observations, the authors suggest finishing all types of immobilization before 1 year of age, when children begin to walk.

Actin Cytoskeleton↗

PubMed1990

Immunoelectron microscopic observations on tropomyosin localization in striated muscle.

Tropomyosin localization in striated muscle was studied by means of immunoelectron microscopy. Polyclonal and monoclonal antibodies to tropomyosin were allowed to diffuse into mechanically skinned single fibres dissected from frog semitendinosus muscle. Antibodies produced transverse I-band stripes with the expected periodicity of 38 nm. However, some differences were revealed among the various antibodies. While polyclonal antibodies generally showed 23 stripes, monoclonal antibodies showed an extra 24th stripe immediately adjacent to the Z-line, implying some structural/functional uniqueness of this terminal tropomyosin. Furthermore, the stripes did not always lie parallel to the Z-line. When the Z-line was straight or slightly skewed, the stripes generally were parallel to it. However, when Z-line skew was more severe, the stripes remained perpendicular to the fibre axis, indifferent to the Z-line skew. This may implay that the coupling of tropomyosin to the thin filament is not tight. Finally, the monoclonal antibodies themselves exerted an anomalous effect on the Z-line, apparently extracting or shifting some of its mass.

Animals↗

PubMed1990

A-band shortening in single fibers of frog skeletal muscle.

The question of whether A-bands shorten during contraction was investigated using two methods: high-resolution polarization microscopy and electron microscopy. During shortening from extended sarcomere lengths in the passive state, sarcomere-length changes were essentially accounted for by I-band shortening. During active shortening under otherwise identical conditions, the sarcomere length change was taken up approximately equally by A- and I-bands. Several potential artifacts that could give rise to apparent A-band shortening were considered and judged unlikely. Results obtained with polarization microscopy were similar to those obtained with electron microscopy. Thus, modest but significant thick filament shortening appears to occur during active sarcomere shortening under physiological conditions.

Animals↗

PubMed1989

Rotational motion of spin labelled microtubule protein.

Microtubule protein, isolated from porcine brain by temperature-dependent assembly-disassembly cycles, was labelled with two types of nitroxide spin labels, maleimide and isothiocyanate. Labelling was performed either in depolymerized or polymerized form of the protein. Electron paramagnetic resonance spectroscopic measurements revealed 34 ns rotational correlation time of the labels in disassembled microtubule protein which corresponds most likely to the rotational motion of the subunits. Upon polymerization, changes in the rotational dynamics of microtubule protein occurred in the temperature range of 20-30 degrees C. Polymerization process was revealed as a transition between two states, one characterizing the tubulin in its monomeric form and the other the polymeric form. In the temperature range of 20-30 degrees C, both forms (monomer-polymer) of tubulin were observed. Very slow rotational motion in the millisecond time range was detected in microtubule pellet. Orientation dependence in the distribution of spin labels in macroscopically oriented microtubules was not found.

Animals↗

PubMed1989

[Problems of the two-stage restoration of flexor tendon injuries. II. Light- and scanning electron microscopy studies of flexor tendon sheaths from hens and from humans].

Authors examined the normal flexor tendon/tendon sheat unit of the toes of the hen and in the zone Verdan 2 of the human hand with light and scanning electron microscope. The fine structure of the synovial membrane was studied with special care. It was found, in accordance with some previous literary data, that the morphology of the hen's and human tenosynovium resemble to each other. The structures of the parietal visceral synovial membranes are described and compared, and the mechanism of the secretion of the synovial fluid is discussed. The results of the present investigations may serve, over the description of the normal anatomical relations, as a comparison to other experiments of two-phase tendon transplantations with the formation of pseudo tendon sheats and also for clinical practice.

Animals↗

PubMed1989

[In vitro study of the marginal closure in adhesive fillings].

The margin closure of Dentin Adhesit composit fillings made in vitro in the dentin cavity is not the best after the cavity cleaning prescribed by the factory. After a cavity cleaning by propiol acid of 1.22% during 10 seconds better marginal closure could be obtained than by using industrial cavity cleanser (Ahydron).

Adhesiveness↗

PubMed1989

[Scanning electron microscopy and microprobe studies of fillings prepared with dentin glue].

The dentin wall of a cavity of class V prepared in vivo was, after a cavity cleaning with phosphorous acid, covered with a composite filling. The filling material penetrated into the dentin tubules. However, it did not adhere to the tubule wall. If the dentin wall of the cavity was cleaned according to factory prescriptions, the filling material did not reach the dentin. Only the preparation debris were impregnated by it.

Adhesives↗

PubMed1989

Longitudinal and vertical ultrastructural lesion of crural muscle in post-thrombotic syndrome.

The vertical and longitudinal ultrastructural changes of the crural muscle (triceps surae) were studied in a selected patient material of 18 patients suffering from post-thrombotic syndrome. The transmission and scanning electron microscopic method helped in revealing that the damage had affected the contractile system, the mitochondria and the endoplasmic reticulum and in addition marked degenerative phenomena occurred. It was shown that vertically the impairments of the fine structure were localized in foci and involved the muscle layers to the same extent. Longitudinally--distally--the muscle changes displayed an increasingly aggravating diffuse appearance. Of the several factors responsible for the development of the pathological ultrastructural picture, tissue hypoxia and metabolic disorder, as well as a decreased microcirculation (hypoperfusion) and chronic inactivity are to be emphasized.

Adult↗

PubMed1988

I-bands of striated muscle contain lateral struts.

In electron micrographs of striated muscle, the I-band often shows a distinct cross-striation. The periodicity of this striation is near 40 nm and has been attributed to troponin, which is localized along the thin filament. However, the cross-striation is often so prominent as to be suggestive of physical structures running transversely across the I-band. We examined I-band ultrastructure using three independent methods: thin sections of chemically fixed specimens; freeze-fracture; and freeze-substitution. With all three methods we found transverse structures distributed throughout the I-band, many of which bridged the gap between neighboring filaments. Such structures were observed in each of the several species studied. In fish muscle in particular, which has a highly regular lattice, it was obvious that these structures gave rise to the observed periodicity.

Animals↗

PubMed1988

Thick filaments of striated muscle are laterally interconnected.

Earlier reports from this and other laboratories indicated that thick filaments may be interconnected along their length by rung-like structures. This study was carried out to test whether these interconnections are genuine structures; whether they appear in different muscle types; and whether they arise from myosin cross-bridges. We studied insect flight muscles because of their well-known ultrastructure, and frog heart and rabbit psoas muscles secondarily. Ultrastructure was examined with freeze-fracture; with conventionally prepared thin sections; and with negative stain. All three methods showed rung-like interconnections between thick filaments. The interconnections spanned the length of the cross-bridge zone, i.e., along all but the central bare zone of the thick filament. They were observed consistently in relaxed, activated, and rigor states. We considered potential artifacts that might cause apparent interconnections where none existed in vivo, but were unable to identify a source of artifact common to all methods. Several features of the interconnections imply that for the most part they may be composed of S-1 heads from adjacent thick filaments binding to one another at their tips.

Animals↗