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Naoto Yagi

Publications and source records attributed to Naoto Yagi.

35 records · Page 2Linked to original sources
PubMed2004

A large-area CMOS imager as an X-ray detector for synchrotron radiation experiments.

The performance of a CMOS flatpanel imager from Hamamatsu Photonics (C7942) has been tested in various synchrotron radiation experiments. This detector has a detection area of about 120 mm x 120 mm with 0.05 mm pixels, and a frame rate of 2 s(-1). The commercially available product was insensitive to X-rays with an energy lower than 15 keV, but slight modifications solved this problem. Images obtained in small-angle scattering, protein crystallography and medical imaging experiments were all of high quality. The fast readout and the large area are advantageous in real-time imaging. Although its noise level is higher than the area detectors that are currently used in synchrotron radiation experiments, it is particularly useful in experiments where other bulky detectors cannot be used. Its relatively low price (about 30,000 US dollars) makes it a unique option in the choice of detectors.

Animals↗
PubMed2004

In situ measurements of crossbridge dynamics and lattice spacing in rat hearts by x-ray diffraction: sensitivity to regional ischemia.

BACKGROUND: Synchrotron radiation has been used to analyze crossbridge dynamics in isolated papillary muscle and excised perfused hearts with the use of x-ray diffraction techniques. We showed that these techniques can detect regional changes in rat left ventricle contractility and myosin lattice spacing in in situ ejecting hearts in real time. Furthermore, we examined the sensitivity of these indexes to regional ischemia. METHODS AND RESULTS: The left ventricular free wall of spontaneously beating rat hearts (heart rate, 290 to 404 bpm) was directly exposed to brief high-flux, low-emittance x-ray beams provided at SPring-8. Myosin mass transfer to actin filaments was determined as the decrease in reflection intensity ratio (intensity of 1,0 plane over the 1,1 plane) between end-diastole and end-systole. The distance between 1,0 reflections was converted to a lattice spacing between myosin filaments. We found that mass transfer (mean, 1.71+/-0.09 SEM, n=13 hearts) preceded significant increases in lattice spacing (2 to 5 nm) during systole in nonischemic pericardium. Left coronary occlusion eliminated increases in lattice spacing and severely reduced mass transfer (P<0.01) in the ischemic region. CONCLUSIONS: Our results suggest that x-ray diffraction techniques permit real-time in situ analysis of regional crossbridge dynamics at molecular and fiber levels that might also facilitate investigations of ventricular output regulation by the Frank-Starling mechanism.

Actin Cytoskeleton↗
PubMed2004

Sarcomere-length dependence of lattice volume and radial mass transfer of myosin cross-bridges in rat papillary muscle.

We examined the sarcomere length-dependence of the spacing of the hexagonal lattice of the myofilaments and the mass transfer of myosin cross-bridges during contraction of right ventricular papillary muscle of the rat. The lattice spacing and mass transfer were measured by using X-ray diffraction, and the sarcomere length was monitored by laser diffraction at the same time. Although the lattice spacing and the sarcomere length were inversely related, their relationship was not exactly isovolumic. The cell volume decreased by about 15% when the sarcomere length was shortened from 2.3 micro m to 1.8 micro m. Twitch tension increased with sarcomere length (the Frank-Starling law). At the peak tension, the ratio of the intensity of the (1,0) equatorial reflection to that of the (1,1) reflection was smaller when the tension was greater, showing that the larger tension at a longer sarcomere length accompanies a larger amount of mass transfer of cross-bridges from the thick to the thin filament. The result suggests that the Frank-Starling law is due to an increase in the number of myosin heads attached to actin, not in the average force produced by each head.

Animals↗
PubMed2004

Intensity of X-ray reflections from skeletal muscle thin filaments partially occupied with myosin heads: effect of cooperative binding.

For quantitative analysis of contractile proteins of muscle by means of X-ray diffraction, it is important to know how the intensities of individual reflections are related to the number of diffracting objects, i.e., the amount of constituent contractile protein in the muscle cell. Here we diffused various amounts of exogenous myosin subfragment-1 (S1) into overstretched skinned skeletal muscle fibers, either in the presence or absence of Ca2+ , and derived the relationship between the S1 content and the intensities of reflections arising from the S1. In theory, the intensities should be proportional to the square of the S1 content (square law). However, the intensity-content relation deviated systematically from the square law as the S1 content was lowered, and it was better described as a linear function at the lower end of the S1 contents (<20% of saturation level). Model calculations show that the way of deviation is explained by the cooperative manner of S1 binding to the regulated thin filament.

Actins↗
PubMed2004

X-ray diffraction from a left ventricular wall of rat heart.

We studied x-ray diffraction from the left ventricular wall of an excised, perfused whole heart of a rat using x rays from the third-generation synchrotron radiation facility, SPring-8. With the beam at right angles to the long axis of the left ventricle, well-oriented, strong equatorial reflections were observed from the epicardium surface. The reflections became vertically split arcs when the beam passed through myocardium deeper in the wall, and rings were observed when the beam passed into the inner myocardium of the wall. These diffraction patterns were explained by employing a layered-spiral model of the arrangement of muscle fibers in the heart. In a quiescent heart with an expanded left ventricle, the muscle fibers at the epicardium surface were found to have a (1,0) lattice spacing smaller than in the rest of the wall. The intensity ratio of the (1,0) and (1,1) equatorial reflections decreased on contraction with a similar time course in all parts of the wall. The results show that it is possible to assign the origin of reflections in a diffraction diagram from a whole heart. This study offers a basis for interpretation of x-ray diffraction from a beating heart under physiologically and pathologically different conditions.

Animals↗
PubMed2004

In vitro evaluation of normal and abnormal lungs with ultra-high-resolution CT.

Synchrotron radiation microtomography is a new technique with high directionality of a synchrotron radiation beam and a high-resolution detector array. In this study, we estimated the visualization of the peripheral human lung structure with an ultra-high-resolution computed tomography (CT) system, the synchrotron radiation CT. The synchrotron radiation CT system uses the bending magnet beamline emitted from the 8.0 GeV electron storage ring. Six lung specimens were obtained at autopsy: 3 normal, 1 cellular alveolitis, 1 diffuse alveolar damage, and 1 pulmonary hemorrhage. Each specimen was cut down to a cylindrical sample with 6-mm diameter and 15- to 25-mm height. The synchrotron radiation CT images of these lung samples were obtained using the ultra-high-resolution image detector system with a charge coupled device (CCD) array detector (1024 x 1024 pixels with 12 x 12 microm2 pixel size). After that, the sample specimens were sliced to 200 microm (micrometer) thickness, and were observed with a stereomicroscope and by contact radiography. Finally, approximately 10-microm thick microscopic images were obtained and compared with the synchrotron radiation CT images. The synchrotron radiation CT could depict the peripheral lung including peripheral airways, airspaces, and alveolar walls individually. Each finding in the 3 disease processes seen on the synchrotron radiation CT images correlated well with the microscopic findings. The synchrotron radiation CT allows microtomographic imaging of human lung specimens with ultra high-spatial resolution (12 microm) on a level approaching that of conventional histopathology, without sectioning.

Humans↗
PubMed2004

Structural transients of contractile proteins upon sudden ATP liberation in skeletal muscle fibers.

Structural changes of contractile proteins were examined by millisecond time-resolved two-dimensional x-ray diffraction recordings during relaxation of skinned skeletal muscle fibers from rigor after caged ATP photolysis. It is known that the initial dissociation of the rigor actomyosin complex is followed by a period of transient active contraction, which is markedly prolonged in the presence of ADP by a mechanism yet to be clarified. Both single-headed (overstretched muscle fibers with exogenous myosin subfragment-1) and two-headed (fibers with full filament overlap) preparations were used. Analyses of various actin-based layer line reflections from both specimens showed the following: 1), The dissociation of the rigor actomyosin complex was fast and only modestly decelerated by ADP and occurred in a single exponential manner without passing through any detectable transitory state. Its ADP sensitivity was greater in the two-headed preparation but fell short of explaining the large ADP effect on the transient active contraction. 2), The decay of the activated state of the thin filament followed the time course of tension more closely in an ADP-dependent manner. These results suggest that the interplay between the reattached active myosin heads and the thin filament is responsible for the prolonged active contraction in the presence of ADP.

Actomyosin↗
PubMed2003

Electron density measurement with dual-energy x-ray CT using synchrotron radiation.

Monochromatic x-ray computed tomography (CT) at two different energies provides information about electron density of human tissue without ambiguity due to the beam hardening effect. This information makes the treatment planning for proton and heavy-ion radiotherapy more precise. We have started a feasibility study on dual energy x-ray CT by using synchrotron radiation. A translation-rotation scanning CT system was developed for quantitative measurement in order to clarify what precision in the measurement was achieved. Liquid samples of solutions of K2HPO4 and solid samples of tissue equivalent materials were used to simulate human tissue. The experiments were carried out using monochromatic x-rays with energies of 40, 70 and 80 keV produced by monochromatizing synchrotron radiation. The solid samples were also measured in a complementary method using high-energy carbon beams to evaluate the electron densities. The measured electron densities were compared with the theoretical values or the values measured in the complementary method. It was found that these values were in agreement in 0.9% on average. Effective atomic numbers were obtained as well from dual-energy x-ray CT. The tomographic image based on each of the electron densities and the effective atomic number presents a different feature of the material, and its contrast drastically differs from that in a conventional CT image.

Connective Tissue↗
PubMed2003

Bone structure and mineralization demonstrated using synchrotron radiation computed tomography (SR-CT) in animal models: preliminary findings.

We investigated the ability of synchrotron radiation computed tomography (SR-CT) to demonstrate trabecular microstructure, detail of trabecular surfaces, and mineralization of bones. Eight rat vertebrae, six rat tibiae, and eight minipig vertebrae were scanned using SR-CT at the synchrotron radiation facility Super Photon ring-8GeV (SPring-8). Images obtained using conventional micro-CT, scanning electron microscopy (SEM), and contact microradiography (CMR) were compared with the SR-CT images. SR-CT showed high image quality without visible partial volume effect. Three-dimensional SR-CT revealed shallow concavities in the bone surface, which were considered to correspond to osteoclastic resorption areas, as well as the connectivity, anisotropy, and shape (rod- or platelike) of trabeculae. Two-dimensional SR-CT showed different density along the surface of the trabecular bone, indicating the degree of bone mineralization. In conclusion, SR-CT seems to be a useful tool for delineating trabecular surfaces, evaluating bone mineralization, and revealing precise trabecular structure.

Animals↗
PubMed2003

Static and dynamic x-ray diffraction recordings from living mammalian and amphibian skeletal muscles.

Static and time-resolved two-dimensional x-ray diffraction patterns, recorded from the living mouse diaphragm muscle, were compared with those from living frog sartorius muscle. The resting pattern of mouse muscle was similar to that of frog muscle, and consisted of actin- and myosin-based reflections with spacings basically identical to those of frog. As a notable exception, the sampling pattern of the myosin layer lines (MLL's) indicated that the mouse myofilaments were not organized into a superlattice as in frog. The intensity changes of reflections upon activation were also similar. The MLL's of both muscles were markedly weakened. Stereospecific (rigorlike) actomyosin species were not significantly populated in either muscle, as was evidenced by the 6th actin layer line (ALL), which was substantially enhanced but without a shift in its peak position or a concomitant rise of lower order ALL's. On close examination of the mouse pattern, however, a few lower order ALL's were found to rise, slightly but definitely, at the position expected for stereospecific binding. Their quick rise after the onset of stimulation indicates that this stereospecific complex is generated in the process of normal contraction. However, their rise is still too small to account for the marked enhancement of the 6th ALL, which is better explained by a myosin-induced structural change of actin. Since the forces of the two muscles are comparable regardless of the amount of stereospecific complex, it would be natural to consider that most of the force of skeletal muscle is supported by nonstereospecific actomyosin species.

Actins↗
PubMed2003

An x-ray diffraction study on early structural changes in skeletal muscle contraction.

Structural changes in frog skeletal muscle were studied using x-ray diffraction with a time resolution of 0.53-1.02 ms after a single electrical stimulus at 8 degrees C. Tension began to drop at 6 ms (latency relaxation), reached a minimum at 8 ms, and then twitch tension developed. The intensity of the meridional reflection at 1/38.5 nm(-1), from troponin molecules on the thin filament, began to increase at 4-5 ms and reached a maximum at approximately 12 ms. The meridional reflections based on the myosin 43-nm repeat began to decrease when the tension began to develop. The peak position of the third-order myosin meridional reflection began to shift toward the higher angle at approximately 5 ms, reached a maximum shift (0.02%) at 10 ms, and then moved toward the lower angle. The intensity of the second actin layer line at 1/18 nm(-1) in the axial direction, which was measured at 12 degrees C, began to rise at 5 ms, whereas the latency relaxation started at 3.5 ms. These results suggest that 1), the Ca(2+)-induced structural changes in the thin filament and a structural change in the thick filament have already taken place during latency relaxation; and 2), the Ca(2+) regulation of the thin filament is highly cooperative.

Actins↗
PubMed2003

An x-ray diffraction study on the ADP-induced conformational change in skeletal muscle myosin.

Effects of ADP on the conformation of myosin cross-bridges were studied in x-ray diffraction experiments on single skinned fibers of frog skeletal muscle by photorelease of ADP from caged-ADP. The experiments were performed at the third-generation synchrotron radiation facility SPring-8 with a time resolution of 5 ms. The intensity of the third-order meridional reflection from myosin filaments (at 1/14.4 nm(-1)) increased promptly after the ADP release with a time constant smaller than 5 ms, which was similar to that of tension decline. The results show that ADP binding induces a conformational change of myosin in skeletal muscle fibers.

Adenosine Diphosphate↗
PubMed2002

Wavelength-dispersive total-reflection X-ray fluorescence with an efficient Johansson spectrometer and an undulator X-ray source: detection of 10-16 g-level trace metals.

The present paper reports significant enhancement of the detection power for total-reflection X-ray fluorescence (TXRF). The employment of an efficient wavelength-dispersive spectrometer rather than a conventional Si(Li) detector, as well as the use of a quasi-monochromatic undulator X-ray source, completely changed the quality of X-ray florescence spectra. The energy resolution is 20 times better, which effectively contributes to reducing the low-energy tail of the scattering background and to separating neighboring X-ray florescence peaks. Another advantage is its capability with respect to high-counting-rate measurements, which ensure the detection of weak signals from trace materials. The absolute and relative detection limit for nickel are 3.1 x 10(-16) g and 3.1 ppt (pg/g) for a 0.1-microL droplet of pure water, respectively, which is nearly 50 times better than the current best data achieved by conventional energy-dispersive TXRF using a Si(Li) detector system.

Equipment Design↗
PubMed2002

X-ray refraction-enhanced imaging and a method for phase retrieval for a simple object.

Refraction-enhanced imaging is now widely used for imaging low-absorption-contrast specimens in the hard X-ray region. However, the interpretation of the details of a refraction-enhanced image is not always clear. In this paper the theoretical treatment of refraction-enhanced imaging and a method for phase retrieval from refraction-contrast images are discussed in comparison with angular-deflection mapping of the transmitting beam. The problems of thick and complicated objects are also discussed.

Birefringence↗
PubMed2002

Radial mass transfer of cross-bridges in a tetanized ferret heart muscle.

An X-ray diffraction experiment on ferret heart muscle was made to examine the relationship between tension and mass transfer from the thick to the thin filament associated with the interaction of cross-bridges with actin. A ferret papillary muscle was electrically stimulated for 8 s in the presence of 5 microM ryanodine to give a tetanus. At different extracellular Ca2+ concentrations (2-20 mM), a linear relationship was found between the tension and the mass transfer. It was concluded that a change in tension caused by altering the extracellular Ca2+ concentration is due to a change in the number of myosin heads bound to actin. This is in contrast to the results obtained on skinned preparations, which showed a markedly nonlinear relationship between the number of heads in the vicinity of the thin filaments and force. It was found that the tension per myosin head is similar in twitch and tetanus of cardiac muscle. Also, a similar fraction of myosin heads is recruited in tetanus of cardiac and skeletal muscles.

Aequorin↗
PubMed2002

Time-resolved X-ray diffraction reveals movement of F helix of D96N bacteriorhodopsin during M-MN transition at neutral pH.

D96N bacteriorhodopsin has two photointermediates with the deprotonated Schiff base: the M and MN intermediates. We measure the time-resolved x-ray diffraction of the D96N purple membrane after flash photoexcitation (pH 7.0, 25 degrees C). The data clearly show the M-MN transition during the D96N photocycle. Low-resolution projection maps of these states show that the F helix of the MN intermediate shifts from its original position and this shift is much larger than that of the M intermediate. This indicates that the F helix moves in the M-MN transition of the D96N bacteriorhodopsin photocycle. Moreover, the existence of the MN intermediate in the D96N photocycle under neutral pH indicates that the MN intermediate is not peculiar to the alkaline condition. It is notable that the structural transition of M-MN is independent of the protonation state of the Schiff base. Therefore, the F helix movement precedes reprotonation of the Schiff base in the bacteriorhodopsin photocycle. Our previous study showed that the M-MN transition is hydration-dependent and that the MN intermediate is more hydrated than the M intermediate. Considering this together with the present results, we conclude that the movement of the F helix causes hydration of the cytoplasmic side, which promotes the reprotonation of the Schiff base.

Amino Acid Substitution↗