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Biomedical subjects

H Sugi

Publications and source records attributed to H Sugi.

At least 127 records · Page 7Linked to original sources
PubMed1985

Differential effects of sinusoidal vibrations on tension and stiffness in Mytilus smooth muscle during catch state.

Sinusoidal vibrations (10-100 Hz, 0.5-2.5%) reduced catch tension in the anterior byssal retractor muscle of Mytilus edulis, while the stiffness measured as the tension increment in response to the stretch phase of vibration did not change appreciably, indicating that the vibration-induced reduction of catch tension may not be simply explained as being due to the detachment of cross-links between actin and myosin.

Animals↗
PubMed1985

Force-velocity relation in paired frog sartorius muscles attached to opposite lever arms.

To study the mechanism of the longitudinal stability at the level of whole muscles, paired frog sartorius muscles were attached to the opposite lever arms at unequal distances from the pivot. The lever was initially fixed in position, and when the full isometric forces were developed in both muscles, it was released to move, the result being that the advantaged muscle shortened by stretching the disadvantaged one with a nearly constant velocity depending on the ratio between their points of attachment from the pivot. The force-velocity relation of the advantaged muscle was virtually identical with the ordinary force-velocity relation obtained from the isotonic release experiments, while the force-velocity relation of the disadvantaged muscle was found to be entirely different from the ordinary one because of a marked increase in the load-bearing ability. These results are discussed in connection with the enhancement of mechanical performance in lengthening muscle.

Animals↗
PubMed1984

Cinematographic studies on the A-band length changes during Ca-activated contraction in horseshoe crab muscle myofibrils.

Cinematographic recordings of sarcomere shortening were performed on glycerinated horseshoe crab muscle myofibrils during Ca-activated contraction. When the preparations at slack length (sarcomere length, 7-9 microns) were locally activated with iontophoretically applied Ca ions, the A-band length did not change appreciably while the activated sarcomeres shortened linearly with a velocity similar to the maximum shortening velocity measured on intact muscle fibers. If, on the other hand, previously stretched preparations (sarcomere length, 11-14 microns) were locally activated, the A-band length first increased by 40-50% and then shortened to the initial length, while the activated sarcomeres continued to shorten. These results indicate that the thick filament shortening may not be associated with the physiological sarcomere shortening; the transient A-band lengthening with long initial sarcomere lengths may result from the transient misalignment of the thick filaments followed by their realignment, implying that the force exerted by the cross-bridge is not constant but may vary according to its past history.

Animals↗
PubMed1984

Factors affecting the equatorial X-ray diffraction pattern from contracting frog skeletal muscle.

Changes in the equatorial X-ray diffraction pattern from tetanized frog sartorius muscles (Rana catesbiana ) were studied by use of time-resolved data collection technique (time resolution, 0.5 sec) to give information about the dynamic properties of the cross-bridges. No significant changes in the intensity ratio of two equatorial reflections (I1,0/I1,1) were observed when isometrically contracting muscles were slowly stretched by 5-6%, in spite of marked force changes. The intensity ratio also showed no significant changes when the load on isometrically contracting muscles was suddenly increased from Po to 1.2-1.5 Po to produce isotonic muscle lengthening. Closer examination of the data indicated that a small decrease in the value of I1,1 was caused by both slow stretch and isotonic lengthening. Because of the scatter of experimental plots in I1,0, the effect of small change in I1,1 on the intensity ratio fell within the range of accuracy of measurement. It is suggested that no marked changes in myosin head orientation or in the number of the cross-bridges in the vicinity of the thin filaments take place in response to slow stretches or isotonic lengthening, and that the decreased regularity of the filament lattice may produce the change in I1,1.

Animals↗
PubMed1984

Sarcomere length and force changes in single tetanized from muscle fibers following quick changes in fiber length.

By use of an optical system, with which the beam of the first-order diffraction line of He-Ne laser light from a single frog skeletal muscle fiber was split by the wedge-shaped mirror to be focused on two photodiodes ( Haugen & Sten - Knudsen , 1976), small changes in sarcomere length (less than 1 A) could be recorded during quick fiber length changes (up to 1.2% of Lo, complete within 0.2-0.4 msec) applied at the plateau of isometric tetanus. Data were only obtained on fibers which showed typical sinusoidal sarcomere length changes in response to sinusoidal fiber length changes during tetanus with a linear relation between their magnitudes. Measurements of sarcomere length changes were made at various points along the fiber length. The interval between the onset of fiber length changes at one fiber end and that of force change recorded at the fixed fiber end was explained by the propagation of mechanical impulse at about 180 m/sec. In the case of quick releases, the onset of sarcomere shortening near the fixed fiber end tended to take place after that of force change, especially with long fibers, indicating that the drop in force during a quick release may not always be associated with sarcomere shortening along the entire fiber length. This implies that the force changes in response to rapid length changes may not give correct information about the cross-bridge properties. Irrespective of the point at which sarcomere shortening was recorded, it was always observed that the onset of quick force recovery occurred while sarcomere shortening was still in progress. Such a phenomenon can be simulated by a viscoelastic multi-segment model with series elasticity located in each segment.

Animals↗
PubMed1984

Muscle stiffness changes during isometric contraction in frog skeletal muscle as studied by the use of ultrasonic waves.

In order to measure muscle stiffness changes with a high time resolution and with minimal disturbance to the contractile mechanism per se, we constructed an apparatus with which the propagation velocity of ultrasonic waves (MHz region) in the longitudinal or transverse direction was measured to serve as a measure of muscle stiffness. The longitudinal muscle stiffness started to increase on stimulation before the onset of isometric force, and reached a maximum before the peak twitch force. Analysis of experimental data indicated that, during an isometric tetanus, the increment of muscle longitudinal stiffness was about 6 X 10(7)N/m2, a value similar to those obtained by Truong (1974) and Ford et al. (1981) with sinusoidal vibrations (3 kHz) and length steps respectively. This suggests that the increment of muscle longitudinal stiffness during the activation of the contractile system results from the recruitment of an almost non-dispersive elastic component. In the case of transverse muscle stiffness, on the other hand, it started to decrease on stimulation before the onset of isometric force, and reached a minimum before the peak twitch force. Possible causes of this unexpected result is discussed in relation to the molecular mechanism of muscle contraction.

Animals↗
PubMed1984

Length-dependent changes of pacemaker frequency in the isolated rabbit sinoatrial node.

To correlate changes in pacemaker frequency with those of length and tension in mammalian atrial tissues, a strip of the sinoatrial (SA) nodal tissue (about 10 mm in length and 4 mm in width) isolated from the rabbit heart was subjected to constant-length and constant-load stretches, and the relation between the resulting pacemaker frequency changes and the segmental length changes of the preparation was examined by means of cinematographic recording of the preparation with carbon markers on its surface. The amount of stretch-induced length changes was larger in the perinodal tissue segments than in the SA nodal segments, indicating that the nodal area is less extensible than the perinodal area. The time course of stretch-induced length changes of one nodal segment (closer to the inferior vena cava) was found to roughly parallel that of pacemaker frequency changes, suggesting that the pacemaker frequency is primarily dependent on the length but not on the tension of the SA nodal area.

Animals↗
PubMed1983

Sarcomere length and tension changes in tetanized frog muscle fibers after quick stretches and releases.

The sarcomere length changes in tetanized frog muscle fibers in response to quick fiber length changes were examined along the fiber length with a high-sensitivity laser diffraction technique. The experiments were only performed with muscle fibers in which the uniform orientation and sarcomere length of the component myofibrils were well preserved during a tetanus. When the sarcomere length changes were recorded near the fixed fiber end, the delay of the onset of sarcomere length change in response to the applied fiber length change tended to be longer than that of the onset of tension changes recorded at the fixed fiber end. The magnitude of sarcomere length changes was larger near the moving fiber end than near the fixed fiber end. In the case of quick releases, the resulting sarcomere shortening tended to outlast the fiber shortening, so that the quick tension recovery started during the sarcomere shortening. These results indicate (i) that the tension changes in response to quick fiber length changes may not give direct information about the cross-bridge properties and (ii) that the viscoelastic multisegmental nature of muscle fibers should be taken into consideration in interpreting the tension responses to quick length changes.

Animals↗
PubMed1983

Extensibility of the myofilaments in vertebrate skeletal muscle as revealed by stretching rigor muscle fibers.

The extensibility of the myofilaments in vertebrate skeletal muscle was studied by stretching glycerinated rabbit psoas muscle fibers in rigor state and examining the resulting extension of sarcomere structures under an electron microscope. Although stretches applied to rigor fibers produced a successive yielding of the weakest sarcomeres, the length of the remaining intact sarcomeres in many myofibrils was fairly uniform, being definitely longer than the sarcomeres in the control, nonstretched part of rigor fibers. The stretch-induced increase in sarcomere length was found to be taken up by the extension of the H zone and the I band, whereas the amount of overlap between the thick and thin filaments did not change appreciably with stretches of 10-20%. The thick filament extension in the H zone was localized in the bare regions, whereas the thin filament extension in the I band appeared to take place uniformly along the filament length. No marked increase in the Z-line width was observed even with stretches of 20-30%. These results clearly demonstrate the extensibility of the thick and thin filaments. The possible contribution of the myofilament compliance to the series elastic component (SEC) in vertebrate skeletal muscle fibers is discussed on the basis of the electron microscopic data and the force-extension curve of the SEC in rigor fibers.

Animals↗
PubMed1982

Intracellular calcium translocation during contraction in vertebrate and invertebrate smooth muscles as studied by the pyroantimonate method.

The intracellular localization of activator Ca and its translocation during the mechanical activity were studied on vertebrate and invertebrate smooth muscles by fixing muscle fibers with a 1% OsO4 solution containing 2% potassium pyroantimonate for electron microscopic examination. When guniea-pig taenia coli, Mytilus anterior byssal retractor muscle, and Dorabella longitudinal body wall muscle were fixed during the relaxed state, electron-opaque pyroantimonate precipitate containing Ca was localized along the inner surface of the plasma membrane and at other membranous structures in close apposition to the plasma membrane, in accordance with physiological evidence that these muscles contain intracellularly stored activator Ca. When they were fixed during the contracted state, the precipitate was distributed diffusely in the myoplasm in the form of small particles, indicating the release of activator Ca from the peripheral structures. The contraction in dog coronary artery smooth muscle appears to be associated with the inward movement of extracellular Ca. In accordance with this, the resting coronary artery muscle fibers exhibited the precipitate in the lumen of the caveolae, i.e., the bottle-shaped plasma membrane investigations, but not at the peripheral intracellular structures, though the contracted fibers showed the diffuse distribution of the precipitate in the myoplasm. These results indicate that the pyroantimonate method is very effective in studying the translocation of activator Ca in various types of smooth muscles.

Animals↗
PubMed1982

Physiological and ultrastructural studies on the longitudinal retractor muscle of a sea cucumber Stichopus japonicus. II. Intracellular localization and translocation of activator calcium during mechanical activity.

1. The intracellular localization and translocation of activator Ca in the longitudinal retractor muscle (LRM) of a sea cucumber Stichopus japonicus were studied by fixing the LRM in a 1% OsO4 solution containing 2% K pyroantimonate. 2. In the resting LRM fibres, electron-opaque pyroantimonate precipitate was mostly localized along the inner surface of the plasma membrane and at the subsarcolemmal vesicles in close apposition to the plasma membrane. 3. In the LRM fibres fixed during the mechanical response to ACh and high [K]0, the precipitate was diffusely distributed in the myoplasm in the form of numerous particles with corresponding decrease in the amount of the precipitate at the peripheral structures. 4. Electron probe X-ray microanalysis showed the presence of Ca in the precipitate, indicating that the precipitate provides a valid measure of Ca localization. 5. These results accord with the view that, in the LRM, the contractile mechanism is activated by the release of Ca from the intracellular structures as well as by the inward movement of extracellular Ca.

Acetylcholine↗
PubMed1982

Segmental length changes in stimulated frog sartorius muscle during dynamic mechanical responses.

The nonuniformity of dynamic mechanical responses along the length of stimulated frog sartorius muscle was examined by recording the length changes of muscle segments by means of streak photography. During isometric force development, the central or the pelvic end segment tended to shorten due to the stretching of the other segments. In muscles showing a marked nonuniformity in the segmental length changes occurring during isometric force development, there was also a marked nonuniformity in the segmental length changes occurring during stretches or releases applied at the plateau phase of an isometric tetanus. Marked nonuniform segmental length changes were also observed during afterloaded twitches and tetani. These results indicate that great care should be taken of the muscle segmental nonuniformity in heat and X-ray diffraction studies in which measurements are made using data obtained from a limited region of muscle. During the course of slow stretches or releases applied to tetanized muscles, the tibial and segment exhibited much smaller relative lengthening or shortening than the other segments when it had been appreciably stretched by the other segments during isometric force development. This might be associated with the formation of "locked-on" cross-links in the stretched segment.

Animals↗