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Biomedical subjects

C Nave

Publications and source records attributed to C Nave.

At least 37 records · Page 2Linked to original sources
PubMed1992

[Phase 3 and phase 4 bundle of branch block].

Intermittent left bundle branch blocks are present in the ECGs of 1 patient with mitral valve disease. By occurring either after short or long cycles they represent respectively phase 3 and phase 4 blocks. Such mechanisms emphasize the relationship between automatism and conduction. The occurrence of block and of normal conduction during cycles of the same length, its correlation with the conduction of the previous cycle, demonstrate the presence of a functional linking between successive impulses. This linking may occur every time a potential or active macroreentry circuit exist. In our case the circuit is formed by the 2 bundle branches which join distally in the ventricular septum.

Bundle-Branch Block↗
PubMed1992

[Electric alternans of QRS: its electrophysiologic significance in narrow QRS supraventricular paroxysmal tachycardia].

The results of 22 patient's transesophageal electrophysiologic studies were analyzed to value the meaning of QRS alternans during narrow QRS tachycardia. Standard ECG showed ventricular pre-excitation in eight patients. QRS alternans were in six of them: heart rate was included between 230 and 374 m/sec (301.8 +/- 42 m/sec); in the remaining 16 patients, heart rate was included between 240 and 450 m/sec (350.0 +/- 42 m/sec). Our findings suggest that QRS alternans is related to the rate of tachycardia rather than to the presence of an accessory pathway.

Adult↗
PubMed1991

[Permanent atrial standstill and atrial disease].

A case of permanent atrial standstill suspected upon electrocardiogram is reported, and confirmed by electrophysiological investigation. The originality of this case resides in the fact that the atrial standstill marks the developmental outcome of a bradycardia-tachycardia syndrome. This developmental sequence is the subject on discussion. It is concluded that a combination of auricular muscle lesion and sinus node tissue remains the most plausible anatomical and pathophysiological substratum of the bradycardia-tachycardia syndrome which developed into atrial standstill.

Arrhythmias, Cardiac↗
PubMed1991

[EGG and arrhythmia in subjects with implanted dual-chamber VDD and DDD pacemakers].

The ECGs of four patients with implanted dual chamber VDD and DDD PMKs are shown to demonstrate the difficulty of their interpretation and show some arrhythmias related to dual chamber pacing. In the first patient the DDD PMK caused a high ventricular frequency synchronizing on the atrial fibrillation "f" waves which occurred suddenly some time after PMK implantation; this problem was solved by programming the PMK in VVI. The second and third case, with implanted DDD and VDD PMK respectively, exemplify atrial sensing dysfunction due to atrial catheter displacement. In the fourth patient, with implanted VDD PMK, VDD stimulation periods and VVI ones alternated due to non-adjusted programming. Therefore, the paper re-emphasizes the need for accurate and periodic controls of patients with implanted PMK to correct dysfunction or undesirable patterns of stimulation.

Aged↗
PubMed1987

Pf1 Inovirus. Electron density distribution calculated by a maximum entropy algorithm from native fibre diffraction data to 3 A resolution and single isomorphous replacement data to 5 A resolution.

We have calculated the electron density distribution of the Pf1 strain of filamentous bacteriophage by a maximum entropy method. In the calculation we included native X-ray fibre diffraction data extending to 3 A resolution in the meridional direction on 60 layerlines that are resolved to 4 A in the equatorial direction, and lower resolution data from a single isomorphous derivative iodinated on the Tyr25 residue. The electron density map indicates that the 46-residue protein subunit is a single, gently curved stretch of alpha-helix with its axis at an angle of about 20 degrees to the axis of the virion. The alpha-helix subunit curves around the virion axis by about 1/6 turn, and decreases from about 27 A radius to about 13 A radius in the virion as the amino acid sequence of the subunit runs from the N terminus to the C terminus. Nearest-neighbour alpha-helical subunits are about 10 A apart along their length, and the axis of each subunit makes an unexpected negative angle with its nearest neighbours in the virion. To confirm the validity of the maximum entropy calculation, we have varied the constraints on the calculation. All variations result in either a map that is close to the original map or a map that cannot be interpreted in terms of secondary structure: we find only one map that makes structural sense.

Algorithms↗
PubMed1987

The solution conformations of the subclasses of human IgG deduced from sedimentation and small angle X-ray scattering studies.

The solution conformations of human immunoglobulin G subclass molecules have been investigated by sedimentation and small-angle X-ray scattering techniques. Both methods qualitatively indicate IgG3 to be an extended molecule relative to IgG1. Sedimentation data have been collected for a number of paraproteins of all four subclasses and the hinge-deleted IgG1Dob protein. The known crystal structure of Dob allows the use of this protein as a basis for the proposal of models of the average conformations of IgG subclasses which are consistent with experimental s(0)20,w values. IgG1 is suggested to have a hinge length of 0-15 A and non-coplanar Fab arms; IgG2 to be effectively hingeless with folded-back Fab arms; IgG3 to have an extended hinge of the order of 100 A and IgG4 to be effectively hingeless and T-shaped. The possible correlation of these conformations with subclass function is discussed.

Humans↗
PubMed1987

X-ray diffraction evidence for the existence of 102.0- and 230.0-nm transverse periodicities in striated muscle.

Synchrotron radiation techniques have enabled us to record meridional x-ray diffraction patterns from frog sartorius muscle at resolutions ranging from approximately 2,800 to 38 nm (i.e., overlapping with the optical microscope and the region normally accessible with low angle diffraction cameras). These diffraction patterns represent the transform of the low resolution structure of muscle projected on the sarcomere axis and sampled by its repeat. Altering the sarcomere length results in the sampling of different parts of this transform, which induces changes in the positions and the integrated intensities of the diffraction maxima. This effect has been used to determine the transform of the mass projection on the muscle axis in a quasicontinuous fashion. The results reveal the existence of maxima arising from long-range periodicities in the structure. Determination of the zeroes in the transforms has been used to obtain phase information from which electron density maps have been calculated. The x-ray diffraction diagrams and the resulting electron density maps show the existence of a series of mass bands, disposed transversely to the sarcomere axis and distributed at regular intervals. A set of these transverse structures is associated with thin filaments, and their 102.0-nm repeat suggests a close structural relationship with their known molecular components. A second set, spaced by approximately 230.0 nm, is also present; from diffraction theory one has to conclude that this repeat simultaneously exists in thick and thin filament regions.

Animals↗
PubMed1987

The organisation of collagen fibrils in the human corneal stroma: a synchrotron X-ray diffraction study.

The low angle equatorial diffraction pattern from the human corneal stroma shows that the collagen fibrils have two preferred orientations: inferior-superior and medial-lateral. We have not observed this effect in any other animal species. This arrangement, which was found to be more pronounced in the posterior than in the anterior stroma, was maintained until the last 1 to 2 millimetres before the limbus at which point uniaxial orientation was observed along the circumference. Our interpretation of this result is that most collagen fibrils wrap around the circumference of the cornea and relatively few continue radially into the limbus where uniformity of collagen fibril diameters is lost.

Aged↗
PubMed1986

The superstructure of chromatin and its condensation mechanism. I. Synchrotron radiation X-ray scattering results.

Synchroton radiation X-ray scattering experiments have been performed on chicken erythrocyte chromatin fibres over a wide range of ionic conditions and on various states of the fibres (i.e. "native" in solution, in gels and in whole nuclei; chromatin depleted of the H1 (H5) histones and chromatin with bound ethidium bromide). A correlation between the results obtained with the various chromatin preparations provides evidence for a model according to which at low ionic strength the chromatin fibre already possesses a helical superstructure, with a diameter comparable to that of condensed chromatin, held together by the H1(H5) histone. The most significant structural modification undergone upon an increase of the ionic strength is a reduction of the helix pitch, this leads to condensation in a manner similar to the folding of an accordion. The details of this process depend on whether monovalent or divalent cations are used to raise the ionic strength, the latter producing a much higher degree of condensation. Measurements of the relative increase of the mass per unit length indicate that the most condensed state is a helical structure with a pitch around 3.0-4.0 nm. In this paper we give a detailed presentation of the experimental evidence obtained from static and time-resolved scattering experiments, which led to this model.

Animals↗
PubMed1986

The superstructure of chromatin and its condensation mechanism. II. Theoretical analysis of the X-ray scattering patterns and model calculations.

Model calculations on the superstructure of uncondensed and condensed chromatin are presented. It is found that agreement between the calculated X-ray solution scattering patterns and the experimental observations can be reached with the assumptions that: a) The uncondensed chromatin fibre in solution has a helix-like structure, with a pitch of ca. 33.0 nm, a helical diameter of ca. 20.0 nm and 2.75-3.25 nucleosomes per turn. b) The most condensed state of the chromatin fibre in solution is best represented by a helix-like structure with ca. 2.56 nucleosomes per turn, a pitch of ca. 3.0 nm and a helical diameter of ca. 27.0 nm.

Animals↗
PubMed1986

A synchrotron X-ray diffraction study of bovine cornea stained with cupromeronic blue.

Bovine corneal stroma was stained with the dye Cupromeronic Blue under "critical electrolyte" conditions in order to locate the proteoglycans specifically. Electron microscopy revealed that most of the stained proteoglycan filaments are randomly distributed in the tissue although there are many regions where a close proteoglycan-collagen relationship is evident. On counterstaining the collagen in order to identify the intra-periodic banding pattern, the proteoglycan filaments were seen to predominate at three axial positions within the collagen D-period corresponding to electron-optical staining bands a, c and d/e. X-ray diffraction patterns were obtained from the stained and unstained corneae using a high intensity synchrotron source. Integrated intensities from the meridional patterns were used to calculate a difference electron density distribution which revealed where the collagen was axially modified by the stain. This distribution indicated the presence of the dye periodically associated with the collagen at three major sites, one adjacent to each gap/overlap junction (at electron-optical staining bands a and c) and one in the gap zone (including staining bands d and e). However, the Cupromeronic Blue treatment is estimated to have contributed only about 12% to the variation in electron density along the collagen. The staining also gave rise to a greatly increased level of diffuse background scatter, which, in agreement with the electron-optical observations, indicates that much of the stained material is not ordered with respect to the collagen but is randomly distributed in the tissue.

Animals↗
PubMed1985

Scatter analysis of discrete-sized chromatin fragments favours a cylindrical organization.

Fragments of chromatin containing 23 +/- 2.5 nucleosomes have been fractionated after light nuclease treatment of chicken erythrocyte nuclei. Low-angle scattering measures the total z-average radius of gyration of the already well-defined particles and the shape of scatter curves can be compared with three-dimensional analysis as opposed to cross-section analysis of long chromatin fragments. The data show that the particles are not spherical, have no detectable hole in the center of the structure and are best represented by a solid rod-like shape such as that generated by a coil of nucleosomes with the centre perhaps filled with linker DNA and histone H1/H5. 23 nucleosome fragments, where the DNA is partially fragmented, have near-identical scatter curves to the above-defined intact particles, indicating the primary importance of histone proteins in maintaining the integrity of the chromatin higher-order structure. Neutron scattering shows the radii of gyration to be contrast-independent, which fits in with the model calculations for solenoids. Particles with fragmented DNA and the intact particles, therefore, behave as sections of a solenoidal higher-order structure and possibly are observed as "superbeads' only during the folding and unfolding pathways of nucleosome multimers.

Animals↗
PubMed1985

An X-ray diffraction analysis of rat tail tendons treated with Cupromeronic Blue.

Cupromeronic Blue was used to stain selectively the proteoglycans in rat tail tendons under 'critical electrolyte' conditions. Earlier electron microscopical observations indicated that at least one type of proteoglycan filament is associated with tendon collagen fibrils at the positive staining band 'd'. To ensure that this was not an artefact caused by specimen preparation or the subsequent positive staining of the collagen fibrils, we have analysed low angle meridional diffraction patterns from stained but not dehydrated, embedded or counterstained tissues. Axial electron density profiles of Cupromeronic Blue-stained compared with unstained rat tail tendons revealed the axial locations and relative amounts of dye in both mature and young wet specimens. In mature tendons, the difference electron density profile contained a broad peak centred near residue 180 along the 234-residue D-period. This corresponds to the electron-optical staining band 'd'. In young tendons a similar distribution of stain was observed although in this case there was evidence of a doublet of peaks, one centred near residue 182 (band 'd') and the other near residue 165 (midway between bands d and e1). The wet proteoglycan--Cupromeronic Blue complexes distribute over about 30 nm along the collagen fibril axis. Comparison with the images of filaments seen in the electron microscope suggests that the dye complexes collapse significantly on dehydration and embedding.

Aging↗
PubMed1984

X-ray diffraction studies of tibial plateau cartilage using synchrotron radiation.

X-ray diffraction studies of articular cartilage have been performed using X-rays from two sources: a conventional generator and synchrotron radiation. Blocks of tissue from the tibial plateaux of pigs and dogs were examined to find the orientations of collagen fibrils throughout their depth. Analysis of the resulting diffraction patterns revealed a zonal arrangement of fibrils in both pig and dog tissue. At the articular surface the preferred orientation of fibrils was parallel to the surface, below this was a zone with no obvious preferred orientation and the remaining tissue had fibrils oriented mainly perpendicular to the surface. Using a conventional source of X-rays the exposure time for a single diffraction pattern was a number of days but this was reduced to about 10 min using the more intense synchrotron radiation. This improvement in exposure time facilitates the examination of small areas of tissue. X-ray diffraction using the synchrotron source offers a quick method of determining collagen fibril orientations in small areas of articular cartilage.

Animals↗
PubMed1983

Conformational transitions in oriented fibres of the synthetic polynucleotide poly[d(AT)].poly[d(AT)] double helix.

The synthetic polynucleotide poly[d(AT)].poly[d(AT)] is of interest in studies of the relationship between nucleic acid structure and function. In particular, A + T-rich regions in DNA double helices have been invoked as centres for controlling the transcription of genetic information. Here we describe conditions for observing by X-ray fibre diffraction the A, B, C and D conformations of Na-poly[d(AT)].poly[d(AT)], and for inducing transitions between these conformations. The D form emerges as a particularly stable conformation; once assumed, it persists over a wide range of variation in the relative humidity of the fibre environment. Further, while transitions between the B and D conformations are readily reversible, transitions between A and D are much more complex.

Nucleic Acid Conformation↗
PubMed1983

Maximum-entropy calculation of the electron density at 4 A resolution of Pf1 filamentous bacteriophage.

A 4 A electron-density map of Pf1 filamentous bacterial virus has been calculated from x-ray fiber diffraction data by using the maximum-entropy method. This method produces a map that is free of features due to noise in the data and enables incomplete isomorphous-derivative phase information to be supplemented by information about the nature of the solution. The map shows gently curved (banana-shaped) rods of density about 70 A long, oriented roughly parallel to the virion axis but slewing by about 1/6th turn while running from a radius of 28 A to one of 13 A. Within these rods, there is a helical periodicity with a pitch of 5 to 6 A. We interpret these rods to be the helical subunits of the virion. The position of strongly diffracted intensity on the x-ray fiber pattern shows that the basic helix of the virion is right handed and that neighboring nearly parallel protein helices cross one another in an unusual negative sense.

Bacteriophages↗