Biomedical subjects

H Sugi

Publications and source records attributed to H Sugi.

At least 109 records · Page 6Linked to original sources

PubMed1988

Stiffness changes in frog skeletal muscle during contraction recorded using ultrasonic waves.

1. A technique has been developed with which the stiffness changes in frog skeletal muscle can be continuously recorded by measuring the propagation velocity of ultrasonic waves (3-7 MHz) with negligibly small perturbations to the contractile system. 2. The resting muscle stiffness was 2.256 +/- 0.002 x 10(9) N/m2 (S.D.) at 1-2 degrees C (n = 10) and 2.480 +/- 0.007 x 10(9) N/m2 at 19-20 degrees C (n = 12) in the longitudinal direction, and 2.223 +/- 0.008 x 10(9) N/m2 at 1-2 degrees C (n = 8) and 2.437 +/- 0.007 x 10(9) N/m2 at 19-20 degrees C (n = 9) in the transverse direction. 3. The resting muscle stiffness measured with ultrasonic waves was virtually insensitive to the resting force development, i.e. the extension of the parallel elastic component. 4. The longitudinal muscle stiffness increased during isometric contraction at a rate faster than the force development. The amount of increase of the longitudinal stiffness in an isometric tetanus at 2.2 microns sarcomere length was 2.4 +/- 0.1 x 10(7) N/m2 at 1-2 degrees C (n = 10) and 6.5 +/- 1.3 x 10(7) N/m2 at 19-20 degrees C (n = 12). 5. On the other hand, the transverse muscle stiffness decreased during isometric contraction at a rate faster than the force development. The amount of decrease of the transverse stiffness in an isometric tetanus at 2.2 microns sarcomere length was 5.6 +/- 0.1 x 10(7) N/m2 at 1-2 degrees C (n = 8) and 6.4 +/- 0.3 x 10(7) N/m2 at 19-20 degrees C (n = 9). 6. The amount of both the longitudinal and the transverse stiffness changes during an isometric tetanus decreased linearly with increasing sarcomere length, indicating that the stiffness changes during contraction reflect the formation of cross-links between the myofilaments. 7. Both the longitudinal and the transverse stiffness increased when resting muscle was put into rigor state. The rigor muscle stiffness was insensitive to small stretches, i.e. the strain of the rigor cross-links. 8. These results are discussed in connection with the behaviour of cross-bridges during isometric contraction and in rigor.

Animals↗

PubMed1988

Stiffness changes during enhancement and deficit of isometric force by slow length changes in frog skeletal muscle fibres.

1. The mechanism of the enhancement and the deficit of isometric force by slow length changes in frog fast muscle fibres was studied by recording muscle fibre stiffness changes as measured with sinusoidal vibrations (0.5-1.9 kHz, peak-to-peak amplitude 0.1% of slack length, L0). 2. When a tetanized fibre was slowly stretched by 5-9% from sarcomere lengths 2.4-2.6 microns, the force rose to a peak during the stretch and then decreased towards a steady level higher than that during the ordinary isometric tetanus at the same sarcomere length. 3. The stiffness of the fibre first rose abruptly in response to stretch and then started to decrease linearly while the stretch went on; after the completion of stretch the stiffness decreased towards a steady value which was equal to that during the isometric tetanus at the same sarcomere length, indicating that the enhancement of isometric force is associated with decreased stiffness. 4. If a tetanized fibre was slowly released by 4-12% from sarcomere lengths 2.55-2.7 microns, the steady force attained after the completion of release was lower than that during an isometric tetanus at the same sarcomere length. 5. The stiffness of the fibre changed in parallel with the force both during and after the applied release. 6. Recordings of the segmental length changes along the fibre with a high-speed video system (200 frames/s) indicated that all segments lengthened in response to the applied stretch. 7. The segmental length changes in response to the applied release were markedly non-uniform; the length of a segment located at the centre of the fibre did not change appreciably both during and after the release. 8. These results are discussed in terms of cross-bridge performance and structure of the myofilament lattice.

Animals↗

PubMed1988

Time-resolved X-ray diffraction studies on the effect of slow length changes on tetanized frog skeletal muscle.

1. The mechanism of the enhancement and the deficit of isometric force by slow length changes in frog skeletal muscle was studied with the time-resolved X-ray diffraction technique, using intense X-rays of synchrotron radiation. 2. When a tetanized muscle was slowly stretched by 4% from sarcomere lengths 2.3-2.4 microns, the force rose to a peak during stretch and then decreased to a steady level 10-15% higher than that immediately before stretch. 3. The intensity of the 1,1 equatorial reflection decreased nearly linearly during stretch and then again increased after the completion of stretch, reaching a steady level 12 +/- 5% (mean +/- S.D., n = 11) lower than that immediately before stretch. The above 1,1 intensity change was roughly a mirror image of the force change. 4. The intensity of the 1,0 equatorial reflection showed no marked changes in response to a slow stretch, except for an initial transient increase observed occasionally. 5. If a tetanized muscle was slowly released by 4% from sarcomere lengths 2.3-2.4 microns, the steady force attained after the completion of release was lower than that immediately before release. 6. The 1,1 intensity increased slightly during release, while the 1,0 intensity did not change significantly. 7. The half-width of both the 1,0 and the 1,1 reflections did not change appreciably in response to slow length changes. 8. Slow length changes always produced changes in the spacing between the reflections as expected from the constant-volume behaviour of the myofilament lattice. 9. These results indicate that a slow stretch produces disordering of the myofilament lattice in such a way that the thin filaments are displaced from trigonal positions in the thick filament lattice. The resulting increase in the overall repulsion forces between the filaments may lead to the enhanced isometric force after stretch.

Actin Cytoskeleton↗

PubMed1988

Cooperative interactions of myosin two heads in muscle force generation.

To investigate the possibility of cooperative interactions between the two myosin heads in muscle contraction, Ca2+-activated force development, K+-EDTA- and Mg2+-ATPase activities, muscle fiber stiffness, and the velocity of unloaded shortening were measured on partially p-PDM treated glycerinated muscle fibers, which contained a mixture of myosin molecules with zero, one and two of their heads inactivated. It was found that the magnitude of the Ca2+-activated isometric force development was proportional to the square of both K+-EDTA- and Mg2+-ATPase activities and also to the square of muscle fiber stiffness. If the two myosin heads in the glycerinated fibers are assumed to react independently with p-PDM, the above results strongly suggest that (i) each myosin molecule in the thick filaments can generate force only when its two heads do not react with p-PDM, (ii) muscle fiber stiffness is determined by the total number of native heads, and (iii) there is no cooperative interaction between the two myosin heads in catalyzing ATP hydrolysis.

Adenosine Triphosphatases↗

PubMed1988

Sarcomere length dependence of muscle stiffness changes during contraction recorded using ultrasonic waves.

We have developed a technique with which muscle stiffness changes during isometric contraction can be continuously recorded by measuring the propagation velocity of ultrasonic waves with negligibly small perturbations to the contractile system, and obtained an unexpected result that, during isometric contraction, muscle stiffness decreased in the transverse direction while it increased in the longitudinal direction. In the present study, we measured the stiffness of frog skeletal muscle with ultrasonic waves at various sarcomere lengths from 2.2 to more than 3.6 microns, and found that (1) the resting muscle stiffness is insensitive to the resting force development in both the longitudinal and the transverse directions, and (2) the absolute amount of both the longitudinal and the transverse stiffness changes during isometric tetanus decreased linearly with increasing sarcomere length, approaching zero at 3.6-3.8 microns sarcomere lengths. These results indicate that the stiffness changes measured with ultrasonic waves reflect the changes in the number of cross-links between the myofilaments.

Animals↗

PubMed1988

A self-induced translation model of myosin head motion along thin filament in muscle contraction.

Evidence has been accumulating that muscle contraction may not be associated with the power stroke of the cross-bridges tightly coupled with ATP hydrolysis cycle. We have constructed a new contraction model which includes a number of basic properties of contraction processes not taken into consideration in the models hitherto reported. The basic assumption is that, when one head of a myosin molecule attaches to an actin monomer on thin filament, conformational changes take place in the neighbouring actin monomers to result in their non-symmetrical charge distribution to exert electrostatic force on the unattached head of the same myosin molecule in one direction. Thus, the unattached head moves along thin filament to attach to another actin monomer, while the already attached head detaches from thin filament. These steps are repeated to cause muscle contraction. The above contraction model can explain the results of our X-ray diffraction experiments as well as the results reported by other authors.

Actin Cytoskeleton↗

PubMed1988

31P NMR study of the regulation of glycogenolysis in iodoacetate-treated skeletal muscle.

Extensive in vitro biochemical experiments have established that glycogenolysis is regulated in two different ways; i.e., the Ca regulation at the phosphorylase step and the phosphate-product regulation at the phosphofructokinase step. Recent studies on glycogenolysis in living vertebrate skeletal muscles by use of 31P nuclear magnetic resonance (NMR) presented evidence that glycogenolysis in vivo is regulated by the Ca released from the sarcoplasmic reticulum (SR) but not by the phosphate products. We have performed 31P NMR studies on living frog skeletal muscle, and have shown that glycogenolysis is regulated not only by the Ca from the SR but also by the accumulation of phosphate products by contraction. This indicates that the glycogenolysis in vivo can be actually regulated by the two mechanisms as predicted by in vitro biochemical studies.

Adenosine Triphosphate↗

PubMed1988

Muscle stiffness changes during enhancement and deficit of isometric force in response to slow length changes.

The mechanism of the enhancement and the deficit of isometric force in response to slow length changes in tetanized frog muscle fibers was studied by recording the stiffness changes with sinusoidal vibrations (0.5-1.9 kHz, peak-to-peak amplitude 0.1% of L0). When a tetanized fiber was slowly stretched, the fiber stiffness first rose abruptly and then decreased linearly while the stretch went on; after the completion of stretch, the stiffness decreased towards a steady value which was equal to that during the ordinary isometric tetanus at the same fiber length, though the force decayed towards a steady level higher than that of the ordinary isometric tetanus at the same fiber length. This indicates that the enhancement of isometric force after stretch is associated with decreased stiffness. If, on the other hand, a tetanized fiber was slowly released, the force and the stiffness changed in parallel with each other. Recordings of the segmental length changes along the fiber with a high-speed video system (200 frames/s) indicated that all the segments lengthened in response to slow stretch, while the segmental length changes in response to slow release was markedly nonuniform. These results are discussed in connection with the cross-bridge performance and the filament-lattice structures.

Animals↗

PubMed1987

31P-NMR study of the regulation of glycogenolysis in living skeletal muscle.

Based on in vitro biochemical experiments, it is generally believed that glycogenolysis is regulated in two different ways; i.e., Ca2+ regulation at the phosphorylase step and phosphate-product regulation at the phosphofructokinase step. Recent studies on glycogenolysis in living vertebrate skeletal muscles using 31P nuclear magnetic resonance (NMR) presented evidence that glycogenolysis in vivo is regulated by Ca2+ released from the sarcoplasmic reticulum. We performed 31P-NMR studies on living frog skeletal muscle, and found that glycogenolysis is further regulated by the accumulation of phosphate products by contractile activity. Therefore, glycogenolysis in vivo can actually be regulated by the two mechanisms as predicted by in vitro biochemical studies.

Animals↗

PubMed1986

Evidence for cooperative interactions of myosin heads with thin filament in the force generation of vertebrate skeletal muscle fibers.

To examine the possibility of cooperative interactions between the two myosin heads in muscle contraction, Ca2+-activated force development, K+-EDTA-and Mg2+-ATPase activities, muscle fiber stiffness, and the velocity of unloaded shortening were measured on partially p-phenylenedimaleimide (p-PDM)-treated glycerinated muscle fibers, which contained a mixture of myosin molecules with zero, one, and two of their heads inactivated, and the relationships among these values (expressed relative to the control values) were studied. It was found that the magnitude of the Ca2+-activated isometric force development was proportional to the square of both K+-EDTA- and Mg2+-ATPase activities and also to the square of muscle fiber stiffness. If the two myosin heads in the glycerinated fibers are assumed to react independently with p-PDM, the above results strongly suggest that each myosin molecule in the thick filaments can generate force only when its two heads do not react with p-PDM, muscle fiber stiffness is determined by the total number of native heads, and there is no cooperative interaction between the two myosin heads in catalyzing ATP hydrolysis.

Adenosine Triphosphatases↗

PubMed1986

Time-resolved x-ray study of effect of sinusoidal length change on tetanized frog muscle.

Time-resolved x-ray diffraction studies were done on frog skeletal muscles with synchrotron radiation by applying sinusoidal length changes of frequency 10 Hz and amplitude approximately 1% to isometrically contracting muscles at approximately 17 degrees C. Distinct periodic intensity changes were observed in the 14.3-nm myosin meridional reflection and the equatorial 1,0 and 1,1 reflections. Response of the 14.3-nm reflection to the sinusoidal length change was nonlinear, as evidenced by a large second harmonic in its oscillatory intensity change, whereas the response of the equatorial 1,1 reflection was closely linear, as evidenced by almost sinusoidal intensity change. Intensity change of the 1,0 reflection was nearly antiphase to that of the 1,1 reflection. Integral widths of the 14.3-nm meridional reflection measured along the meridian and of the equatorial 1,1 reflection remained almost constant during tension development, while that of the 1,0 reflection tended to decrease. The widths of the 14.3-nm meridional reflection perpendicular to the meridian and of the equatorial 1,0 reflection appeared to undergo oscillatory changes in response to the sinusoidal length changes.

Animals↗

PubMed1986

Physiological and ultrastructural studies on the mechanism of stretch-induced contractile activation in rabbit cerebral artery smooth muscle.

Quick stretches applied to the helical strips of rabbit cerebral artery produced marked delayed tension development. The stretch-induced contraction was more resistant to the removal of [Ca2+]o and Ca antagonists than the mechanical response to high [K+]o and electrical stimulation, and was absent in chemically skinned preparations, indicating that it is not an inherent property of the contractile mechanism per se. The effect of the removal of [Ca2+]o and drugs such as dantrolene and ryanodine indicated that the intracellular origin of Ca2+ was involved in the stretch-induced contraction. To explore the above possibility, the intracellular Ca localization in rabbit cerebral artery smooth muscle was examined by the pyroantimonate method. In muscle cells fixed at rest, the pyroantimonate precipitate containing Ca was localized along the inner surface of the plasma membrane, while in muscle cells fixed during the stretch-induced contraction the precipitate was diffusely distributed in the myoplasm. These results strongly suggest that the stretch-induced mechanical response is associated with the Ca2+ release from the inner surface of the plasma membrane.

Animals↗

PubMed1986

Structural changes during contraction in vertebrate skeletal muscle as studied by time-resolved X-ray diffraction technique.

To obtain information about the structural changes in vertebrate skeletal muscle during contraction, time-resolved X-ray diffraction studies were performed on the intensity changes of the 59 A and 51 A actin layer lines from bullfrog sartorius muscle during the isometric force development, and the intensity changes of the 143 A and 215 A myosin meridional reflections and of the 1.0 and 1.1 equatorial reflections when isometrically contracting muscle was subjected to sinusoidal length changes (1%, 5-10 Hz) with the following results. The integrated intensities of the 59 A and 51 A actin layer lines increased during the force development by 30-50% for the 59 A reflection, and by about 70% for the 51 A reflection compared to their respective resting values. These intensity changes were greater than those taking place during the transition from rest to rigor state, and observed to precede the intensity changes of the 429 A myosin off-meridional reflection and of equatorial reflections. When sinusoidal length changes were applied to the muscle generating steady isometric force, the resulting periodic intensity changes in the 1.0 and 1.1 equatorial reflections were in phase and in antiphase with the length changes respectively. On the other hand, the 143 A myosin reflection exhibited a characteristic periodic changes; its intensity reached a maximum at each boundary between the stretch and release phases of the length changes. These results are discussed in connection with the behaviour of the cross-bridges during contraction.

Actin Cytoskeleton↗

PubMed1985

Isolation and characterization of calmodulin from a molluscan smooth muscle.

Calmodulin was purified from the anterior byssal retractor muscle (ABRM) of a mollusc Mytilus edulis. Ca2+-induced conformational changes in the ABRM calmodulin could be demonstrated by polyacrylamide gel electrophoresis, by u.v. absorption spectrum and by circular dichroic spectrum. The amino acid composition of the ABRM calmodulin closely resembled that of other invertebrate calmodulins. The ABRM calmodulin was less effective in activating rat brain phosphodiesterase than vertebrate calmodulins.

Amino Acids↗

PubMed1985

Nonsteady motion in unloaded contractions of single frog cardiac cells.

We studied the mode of shortening of enzymatically isolated single frog cardiac cells with a high-speed videosystem to see whether or not shortening is smooth. The segmental shortening of the cell in response to electrical stimulation exhibited a clear pause following the initial shortening over a distance of approximately 11 nm/half-sarcomere. Several preparations showed a second pause following the initial one. Nonsteady motion with a pause lasted usually a few tens of milliseconds. The duration of nonsteady motion was shorter in cells with large velocities of steady shortening following the pause than those with smaller velocities.

Animals↗

PubMed1985

Time-resolved x-ray diffraction studies on the intensity changes of the 5.9 and 5.1 nm actin layer lines from frog skeletal muscle during an isometric tetanus using synchrotron radiation.

Time-resolved x-ray diffraction studies have been made on the 5.9- and 5.1-nm actin layer lines from frog skeletal muscles during an isometric tetanus at 6 degrees C, using synchrotron radiation. The integrated intensities of these actin layer lines were found to increase during a tetanus by 30-50% for the 5.9-nm reflection and approximately 70% for the 5.1-nm reflection of the resting values. The intensity increase of both reflections was greater than that taking place in the transition from rest to rigor state. The intensity change of the 5.9-nm reflection preceded those of the myosin 42.9-nm off-meridional reflection and of the equatorial reflections, as well as the isometric tension development. The intensity profile of the 5.9-nm layer line during contraction was found to be different from that observed in the rigor state.

Actins↗

PubMed1985

Fluorescence properties and contraction characteristics of ANM (N-(1-anilinonaphthyl-4)maleimide)-labeled rabbit psoas muscle fibers.

Fluorescence spectra of ANM-labeled, glycerinated rabbit psoas muscle fibers were recorded in relaxed, contracted, and rigor states. SDS polyacrylamide gel electrophoresis of the ANM-labeled muscle fibers indicated that proteins labeled with ANM were myosin heavy chain, C protein, and actin. In a relaxed state in the presence of ATP, myosin heavy chain was mainly labeled. During the transition from rigor to the relaxed or contracted state, there was a blue shift (about 5 nm) of the ANM emission spectrum. Similar experiments with FAM (N-(3-fluoranthyl)-maleimide)-labeled muscle fibers showed that these fluorescence changes were not artifacts due to the movement of muscle fibers. The fibers labeled in the ATP relaxing solution showed a marked decrease in both isometric force and unloaded shortening velocity (Vo), while in the fibers labeled in the rigor solution isometric tension was not markedly suppressed, though Vo decreased to the same extent as in the fibers labeled in the ATP relaxing solution. Fluorescence spectra of ANM-labeled HMM in different states were also measured. A fluorescence enhancement and a blue shift (about 5 nm) of the emission maximum were observed in HMM + MgATP or HMM + MgATP + F-actin in comparison with HMM + F-actin. These results suggest that the fluorescence spectra of the ANM-labeled muscle fibers reflect their conformational changes between the rigor state (in the absence of MgATP) and the relaxed or contracted state (in the presence of MgATP).

Actomyosin↗

PubMed1985

Susceptibility of intra- and extracellular Mycobacterium avium-intracellulare to cephem antibiotics.

Intra- and extracellular susceptibility of 35 clinically isolated Mycobacterium avium-intracellulare strains to cefotaxime (CTX), ceftizoxime (CZX), and cefoperazone was studied. MICs for 50% of the isolates in vitro were 6.25 micrograms/ml for CTX and CZX and 25 micrograms/ml for cefoperazone. A strain susceptible to CTX (MIC, 0.78 micrograms/ml) and CZX (MIC, 1.56 micrograms/ml) infected human peripheral blood mononuclear cells in the presence of 20% autologous plasma. The mycobacteria replicated exclusively in monocytes under the above culture condition. Concentrations of CZX 1- to 16-fold higher than its in vitro MIC had little effect on intracellular replication of the strain. A concentration of CTX 16-fold higher than its in vitro MIC was bacteriostatic to the mycobacteria, but CTX of lower concentrations showed no effect on intracellular replication. Thus, ineffectiveness of the cephems on the therapy of M. avium-intracellulare infection was suggested.

Cephalosporins↗