Biomedical subjects

R Myklebust

Publications and source records attributed to R Myklebust.

At least 55 records · Page 3Linked to original sources

PubMed1980

Calcium and magnesium levels in isolated mitochondria from human cardiac biopsies.

A non-enzymatic method is presented for isolating mitochondria from small-sized human cardiac samples, including ventricular needle biopsies of 15-25 mg of wet weight. Electron microscopy demonstrates that these fractions are rich in structurally well preserved mitochondria. Calcium and magnesium levels of fractions are determined by atomic absorption flame spectroscopy. Comparative analyses are made in similar fractions of the mouse ventricle. Calcium concentrations of mitocondria isolated in the presence of ruthenium red do not differ significantly between the human auricle and ventricle, averaging 61 nmol Ca/mg protein and 68 nmol Ca/mg protein, respectively. Mitochondrial calcium level is lower in the mouse ventricular fractions, averaging 7 nmol Ca/mg protein. Mitochondrial magnesium amounts to slightly less than 60% of the calcium levels in the human heart, while it exceeds the calcium level by more than 100 per cent in the mouse heart. There is no significant difference of mitochondrial calcium between normal auricles, and, auricles of patients with increased right atrial mean pressure and/or volume overload.

Adult↗

PubMed1979

Effects of isoproterenol on the dense core and perigranular membrane of atrial specific granules.

Following subcutaneous injections of isoproterenol hydrochloride (ISO), atrial cells present a large number of partly degranulated or completely clear "specific granules" enclosed by an intact membrane. Such profiles were never encountered in normal controls and might suggest ISO-induced release of a secretory product. Permeability of perigranular membrane was tested using the extracellular macromolecular tracer horseradish peroxidase (HRP). Reaction product was entirely absent within granules of atrial cells in which the sarcolemma was made permeable to HRP molecules by the ISO injections. This seemed to be the case even in heavily labelled cells in which the peroxidase had penetrated the mitochondrial membranes. In atrial cells impermeable to the tracer, the specific granules closely apposed to the sarcolemma were always HRP-negative. The release mechanism of a possible secretory substance from the specific granules is discussed.

Animals↗

PubMed1979

Ultrastructure of the heart of the sturgeon Acipenser stellatus (Chondrostei).

The ultrastructure of atrial and ventricular myocardial cells from Acipenser stellatus is described. The cells of the atrium are more loosely connected than those of the ventricle. Cell contact is by simple intercalated discs and by desmosomes. The cells are flattened, with peripheral myofibrils and a central region of mitochondria and the nucleus. The sarcoplasmic reticulum consists of subsarcolemmal tubules, that frequently extend towards the central mitochondria. Dyads are small and positioned at any sarcomeric level. No T-tubules are present. Specific granules are restricted to the atrial cell, and are sometimes present within the SR tubules.

Animals↗

PubMed1978

The T-tubule system in the myocardia of the sand rat and mouse as demonstrated by horseradish peroxidase.

The transverse tubule (T-tubule) system in papillary muscles of the sand rat and the mouse were studied with the aid of a diffusion tracer (horseradish peroxidase). The T-tubule system in the sand rat showed a typical mammalian pattern with sarcolemmal tubules invaginating at the Z-band level of the sarcomere. These tubules follow a transverse direction in the cell with frequent longitudinal side-branches which connect tubules at different Z-band levels. In the mouse myocardium, the T-tubules also start as lateral invaginations from the sarcolemma at the Z-band levels. In the cell interior, however, the tubules ramify and brake up into a complicated system of spirally running tubules. These spirals, of relative small diameter (400A--700A), frequently expand and form lobulated cisternae at the Z-band levels.

Animals↗

PubMed1978

Calcium in isolated mitochondria from the left ventricular wall.

The content of calcium per mg mitochondrial protein has been measured by conventional biochemical methods in myocardial tissue of some mammalian species. In addition, a method is presented for (1) the analysis of mitochondrial volumes in the same tissues and (2) calculating the amount of calcium in units of 10(6) mitochondria. It appears that a highly significant correlation exists between the calcium content and the number of mitochondria, with a positive correlation coefficient of 0.92. The mean mitochondrial volume in fractions of the rabbit myocardium was found to be 1.3386 micron3. Electron microscopic studies demonstrate pure mitochondrial fractions and only moderate structural alterations. The method described may represent a useful supplement for the estimation of calcium fluxes in mitochondria and of alterations in their volume, number and structure under conditions of myocardial ischemia.

Animals↗

PubMed1978

Leptomeric fibrils and T-tubule desmosomes in the Z-band region of the mouse heart papillary muscle.

The papillary muscle of the heart of adult white mice is investigated. Intrafibrillary located leptomeric fibrils, frequently encountered in the Z-band region of the myofibrils. The leptomeric fibrils are always running in a transverse direction and often in close proximity to the transverse tubules (which are also located at this level). There seems to be a close connection between the dense striae of the leptofibrils and the Z-bands of ordinary myofibrils. The leptomeric fibrils are spindle-shaped and have a length varying between 0.6 and 1.2 microgrometer. The banding periodicity of the fibrils is approximately 0.16 micrometer. Occasionally desmosomes are observed in the T-tubule system.

Animals↗

PubMed1978

Ultrastructural studies on the formation of myoflilaments and myofibrils in the human embryonic and adult hypertrophied heart.

The myofibrillogenesis in the human embryonic heart is described. The synthesis of thin filaments, which are the first to appear, takes place in close proximity to smooth surfaced SR tubules. Z-band material is closely related to the thin filaments and appears first as irregularly distributed patches in the filamenteous mass. Further cellular differentiation includes an organization of the thin filaments/Z-band material. The synthesis of thick filaments, which follows that of the thin filaments, takes place in ribosome rich areas of the cell. They are rapidly incorporated into the strings of organized thin filaments/Z-band material. The periodic binding sites on both kinds of filaments are believed to play an important role in the precise ordering of the filaments. The formation of myofilaments in the adult hypertrophied human heart is also described. The similarities between this process and that observed in the embryonic heart are striking, and we believe it to be the same process.

Adult↗

PubMed1978

Substructure of inner mitochondrial membranes of myocardial cells as shown by cryo-ultramicrotomy.

The substructure of the inner mitochondrial membranes has been studied by cryo-ultramicrotomy under conditions during which denaturation of proteins by treatment with chemical solutes has been totally avoided. In such preparations, the inner membrane has a substructure consisting of globular subunits. These subunits have an average diameter of ca. 20 A-ca. 62 A and are fairly regularly spaced. Intracristal space is absent in the unstained, freeze-dried preparations, whereas a space of ca 40 A is seen in preparations lightly treated by OsO4-vapour. It is concluded that the subunits of the inner mitochondrial membranes probably consist either of single protein molecules or of complexes of protein molecules.

Animals↗

PubMed1978

Cryofracture of paraffin-embedded heart muscle cells.

A comparative study of internal cellular structures of the sheep ventricular myocardium has been conducted by scanning electron microscopy (SEM) and by transmission electron microscopy (TEM). Access to the cell interior for three-dimensional studies was obtained by cryofracturing paraffin-embedded tissue frozen in liquid nitrogen. For accurate localization of structures of special interest thick paraffin sections were examined in the light microscope (LM). Based on the information gained, it was possible to fracture the block in a desired plane. The fracturing was carried out by a light blow to a precooled scalpel held against the surface of the block, which was immersed in liquid nitrogen. After thawing and deparaffinizing at room temperature in several baths of xylene, the tissue pieces were critical point dried using CO2. As xylene was found to be miscible with CO2, it also served as an intermediate fluid. This method resulted in good preservation fo the myofibrils, mitochondria, sarcoplasmic reticulum and transverse tubules (T-tubules), which was confirmed by TEM studies of conventionally prepared tissue and of tissue originally prepared for SEM.

Animals↗

PubMed1978

Cardiac hypothermia evaluated by ultrastructural studies in man.

Transmural left ventricular biopsies from 13 patients undergoing cardiopulmonary bypass were studied. The hypertrophic myocardium was protected by deep hypothermia (15 degrees C.) during ischemic arrest for a maximal period of 96 minutes. Biopsies were taken at the start of bypass, at the end of aortic cross-clamping, and after 20 minutes of reperfusion. The structure of the mitochondria remained normal, whereas cellular alterations in the form of widened intercalated discs, interstitial and intracellular edema, myelin figures, and slight myofibrillar lysis were observed in all stages. As no clear correlation between these structural injuries and aortic cross-clamping time was seen, they are a result of cardiac hypertrophy rather than intraoperative ischemia.

Adult↗

PubMed1977

Primary 9 + 0 cilia in the embryonic and the adult human heart.

Primary 9 + 0 cilia have been found in the embryonic and the adult human heart. Proximally the cilia show the typical 9 + 0 filament arrangement. Rearrangement of the filaments occur in their distal regions. The cilia are usually found in deep invaginations of the cell membrane, but can also be found in a superficial position. Close connections are frequently found between cilia and thin cytoplasmic extensions from neighbouring cells.

Adult↗

PubMed1977

Calcium containing particles in mitochondria of heart muscle cells as shown by cryo-ultramicrotomy and X-ray microanalysis.

Mitochondria of normal myocardial cells of the sand rat and the mouse as well as of the left ventricle of man, have been examined for their content of calcium. Ultrahistochemistry and X-ray microanalysis revealed two basically different inclusions: Osmiophilic mitochondrial granules and spherical mitochondrial particles. Osmiophilic mitochondrial granules were found in conventionally fixed and plastic embedded tissues as well as in cryosections of chemically fixed and sucrose infused tissues. Such granules lacked inert electron density and probably consisted mainly of unsaturated lipids. X-ray spectra obtained from these tissues revealed no peaks for calcium. Spherical mitochondrial particles were present in dry-cut cryo-sections of N2-frozen tissues not treated by fixatives and/or cryoprotectants. These particles were deeply electron dense in unstained, freeze-dried cryo-sections. They usually measured from 600 A-900 A in diameter in the normal myocardium of the sand rat and the mouse and from 250 A-400 A in diameter in the left ventricular myocardium of man. Significant calcium peaks could be identified in the X-ray spectra of these particles, whereas none occurred in the analyses of other tissue regions. Potassium was detected with about equal frequency in the particles and in other parts of the tissue. On the basis of the inert electron density of the particles and their absence in chemically fixed tissues as well as of the results of the X-ray analysis, it is concluded that they contain precipitates of extremely labile ions of mitochondrial calcium.

Animals↗

PubMed1977

The membrane systems of the cardiac muscle cell of Meganychtiphanes norvegica (m. sars), euphauciacea, crustacea.

The membrane systems of cardiac muscle cells of the euphausiacean Meganychtiphanes norvegica are described. Transverse tubules are found both at the Z-band level (TZ-tubules) and at the H-band level (Th-tubules). Within the sarcomere narrow longitudinal tubules branch off from the TZ-tubules. At the H-band level these tubules expand forming flattened cisternae in dyadic and triadic couplings with the sarcoplasmic reticulum (SR). Adjacent myofibrils are separated by a well developed SR. Modifications of the SR are seen at the H-band level where junctional cisternae are formed.

Animals↗

PubMed1977

The membrane systems of the cardiac muscle cell of Euchaeta norvegica Boeck (crustacea, copepoda).

The membrane systems of the cardiac muscle cell of the copepod Euchaeta norvegica Boeck are described. The heart wall, which is between 0.12 and 1.36 micrometer thick, consists of an epicardium and a single layer of muscle cells. Invaginations of the sarcolemma forming transverse tubules have been found at all levels of the sarcomere with the exception of the H-band level. The longitudinal tubules of the same system are closely associated with the sarcoplasmic reticulum to form interior couplings at the A-I level of the sarcomere. Triadic couplings at the Z band level were not seen in E. norvegica, but peripheral couplings were demonstrated. Nex-uses were found in the intercalated discs.

Animals↗

PubMed1977

Preservation of shock-frozen myocardial tissue as shown by cryo-ultramicrotomy and freeze-fracture studies.

Myocardial tissue was quickly quench-frozen by letting the specimen fall either into liquid nitrogen (LN2) or into LN2-slush, or, by drill-propelling the specimen into LN2 at a speed of 1.5 m/s. The preservation of the tissues was studied in ultrathin, dry-cut and freeze-dried cryo-sections. Shock-freezing by propelling into LN2 yields extensive areas of well preserved tissue without hole damage. Quenching into LN2-slush shows variable results, while a maximum of hole damage is obtained by letting the specimen fall into LN2. Replicas of freeze-fractured tissue which had been quench-frozen by the same methods confirmed these observations. By the drill-propelling, areas 2000-5000 micrometer2 wide reveal good preservation without visible ice crystals. Such areas occur within a superficial band of tissue to a depth of c. 20 micrometer. Even at 35 micrometer and 50 micrometer depth good preservation may be registered at the periphery of the replicas. Description is given of modifications in accessories and methods in order to make the LKB CryoKit more suitable as a routine instrument. These modifications cover replacement of the knife coolant container by a coolant brass container in open connection with three copper tubes, replacement of one of the LKB Dewar flasks by a 25 litre Dewar equipped with a Balzers filling device, and replacement of the LKB plastic sleeve fixed to the back of the specimen coolant container, by two perspex-glass discs mounted in the slit between the Ultrotome base and the cryo-chamber. In addition, modified constructions are presented of the grid-carrier, the press-assembly as well as of the container for freeze-drying and warming up of the frozen sections.

Animals↗

PubMed1976

The membrane systems of the cardiac muscle cell of Tmetonyx cicada O. Fabricius (Crustacea, Amphipoda).

The membrane systems of the cardiac muscle cell of the amphipod Tmetonyx cicada (O. Fabricus) are described. The sarcolemma invaginates and forms a transverse network of tubules at the level of the Z band. Narrow longitudinal tubules branch from the network and connect to another transverse network of tubules at the H band level, where dyadic and triadic junctions are formed with the sarcoplasmic reticulum. Adjacent myofibrils are normally separated by a well developed double layer of the sarcoplasmic reticulum. In areas where the myofibrils closely approach the outer sarcolemma, peripheral couplings have been found at the level of the H band.

Animals↗

PubMed1976

Ultrastructural studies on the growth of filaments and sarcomeres in mechanically overloaded human hearts.

The ultrastructure of myocardial cells was studied in four patients with left ventricular myocardial hypertrophy due to aortic and/or mitral valvular disease. Signs of cellular lysis and synthesis were present in juxtanuclear, interfibrillar, and subsarcolemmal areas. Subsarcolemmal areas contained a granular matrix with foci of polyribosomes, mitochondria, well preserved membranes, a proliferating sarcoplasmic reticulum, and thick and thin filaments and Z-band formations at different stages of development. Z-band substance and thin filaments appeared in the cytoplasm in close proximity to free polyribosomes and endoplasmic membranes and were seemingly not associated with the sarcolemma. These findings were interpreted as evidence for a proteosynthetic activity leading to the formation of new myofibrils and sarcomeres during the chronic stage of hypertrophy. Comparative studies showed that this process has much in common with the genesis of contractile cardiac units in the mammalian embryo. Anomalous Z-band accumulations were studied in normal myocardial cells of various vertebrates and in cells of the overloaded human heart. No evidence of a proteosynthetic activity was detected in the expanded Z-bands.

Adult↗

PubMed1975

Granule containing cells and fibres in the sinus venosus of elasmobranchs.

The concentrations of catecholamines in the heart chambers of elasmobranchs were measured by the fluorimetric method of Bertler et al. (1958). Noradrenaline (NA) can be detected in all the chambers, but the sinus venosus is by far the richest in NA. This can either be due to the presence of storage sites for this amine in the sinus wall, or to a transport of amine to the sinus venosus from the anterior chromaffin bodies. The sinus wall contains large numbers of "granule containing cells" and axon-like processes, both with numerous dense-core vesicles of about 1800 A diameter. The dense-core vesicles contain a uranophilic matrix indicating the presence of protein, phospholipids and/or nucleic acid. The reactions failed to demonstrate amine, which may be due to a loss of amine by diffusion, to a relatively low intravesicular amine concentration, or, to the absence of amines in these granule-containing cells and processes. Heavy accumulations of granule-containing processes occur in the subendothelial area. The endothelium contains fenestrae and pores through which granule-containing fibres protrude into the venous cavity. Granule-containing cells are innervated by presumed cholinergic nerve endings. It is suggested that the granule-containing cells and fibres belong to the neurosecretory system with a cholinergic input, releasing the contents of the dense-core vesicles into the blood stream at the level of the venous cavity.

Acetylcholinesterase↗