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H Sugi

Publications and source records attributed to H Sugi.

At least 73 records · Page 4Linked to original sources
PubMed1993

Essential role of myosin S-2 region in muscle contraction.

We studied the contraction characteristics and Mg-ATPase activity of glycerinated rabbit psoas muscle fibers in the presence and absence of polyclonal antibody directed against the subfragment-2 (S-2) region of myosin, to give information about the role of myosin hinge region in muscle contraction. The antibody was kindly supplied to us from Professor Harrington's laboratory. The antibody-induced decrease of Ca(2+)-activated isometric force development was always accompanied by a parallel decrease of muscle fiber stiffness, so that the stiffness versus force relation remained the same by the antibody treatment. Force-velocity curves, obtained by applying ramp decreases in load from steady isometric force to zero, indicated that the antibody had no effect on the maximum shortening velocity and the shape of the force-velocity curve. Simultaneous measurements of Mg-ATPase activity and Ca(2+)-activated isometric force showed that Mg-ATPase activity of the fibers remained unchanged despite the antibody-induced decrease of isometric force even to zero. These results indicate that, if the antibody attaches to the S-2 region of myosin molecules, their heads still hydrolyze ATP without contributing to both muscle force generation and muscle fiber stiffness.

Animals↗
PubMed1993

Cross-bridge angle distribution and thin filament stiffness in frog skeletal muscle fibers as studied by quick-freeze deep-etch electron microscopy.

To give information about changes in orientation of myosin heads (cross-bridges) during contraction, mechanically skinned frog muscle fibers were rapidly frozen in various states, and cross-bridge angles were measured on the freeze-etch replicas. Histograms of cross-bridge angle distribution showed a peak around 90 degrees in relaxed, contracting and rigor states. The proportion of cross-bridges taking angles around 90 degrees decreased when rigor fibers were stretched or released before freezing. These results are explained by assuming the stretch-induced tilting of cross-bridges due to elastic recoil of the thin filaments in the I-band. As a matter of fact, the axial spacing of actin monomers in the thin filament increased with increasing rigor force before freezing. The stiffness times unit length of the thin filament was estimated to be about 1.8 x 10(4) pN.

Actin Cytoskeleton↗
PubMed1993

Measurement of transverse stiffness change during contraction in frog skeletal muscle by scanning laser acoustic microscope.

The scanning laser acoustic microscope (SLAM) was utilized to measure the change in the propagation velocity in the transverse direction during contraction in living skeletal muscles of the frog. The SLAM was operated at 100 MHz and interferograms were produced on a CRT in real time. The images of the interferogram were processed by image-analyzer and the propagation velocity was calculated from the shift of the interference line at rest and during contraction. In all the measurements (n = 15), the velocities during contraction were clearly slower (-7.6 m/s) than at rest and this means that the transverse stiffness decreased during contraction (-2.4 x 10(7) N/m2). The decrease in the propagation velocity preceded the increase in force by 30-40 ms after stimulation, suggesting that the decrease in the transverse stiffness reflects the basic molecular change in muscle contraction.

Animals↗
PubMed1993

Relation between magnetically-applied force and velocity in beads coated with rabbit myosin, sliding on actin cables in Nitellopsis cells.

We have succeeded in controlling the sliding movement of myosin-coated magnetizable beads on actin cables in Nitellopsis cells by the inhomogeneous magnetic field adjacent to a small, strong permanent magnet. The relation between magnetic force acting on the bead and the bead velocity was, in many respects, similar to that obtained from the same system by the use of centrifugal force (Oiwa et al., 1990). In particular, force favouring the motion (negative load) had little effect on the velocity until it was sufficient to pull the bead off the actin, whereas a relatively small positive load caused a reduction in velocity to a plateau value. Although the present method does not allow a good control of force direction, it demonstrates the promise of magnetic force in studying in vitro motility.

Actins↗
PubMed1993

Unitary distance of actin-myosin sliding studied using an in vitro force-movement assay system combined with ATP iontophoresis.

To obtain information about the mechanism of ATP-dependent actin-myosin sliding responsible for muscle contraction, we studied the "unitary" distance of sliding between a myosin-coated glass microneedle and actin filament arrays (actin cables) in a giant algal cell induced by iontophoretic application of ATP, attention being focused on the minimum distance of ATP-induced sliding when the amount of applied ATP was gradually decreased in the presence of hexokinase and D-glucose. The number of myosin heads interacting with actin cables was reduced to less than 100, as judged from the maximal force Po (approximately 100 pN) generated by myosin heads on the needle in the presence of 2 mM ATP. When the amount of iontophoretically applied ATP was decreased by reducing the amount of charge passed through the ATP electrode from 80 to 2 nC, the distance of ATP-induced actin-myosin sliding decreased almost linearly from approximately 100 to approximately 10 nm, no detectable actin-myosin sliding being observed with further reduction of the charge passed through the electrode. The amount of external load exerted by the bent microneedle was less than 1% of Po for the sliding distance < 50 nm. The actin-myosin sliding distances with a small amount of ATP slightly above the amount required to induce the minimum sliding distance were distributed around integral multiples of 10 nm, suggesting that the unitary distance of actin-myosin sliding coupled with ATP hydrolysis is of the order of 10 nm.

Actins↗
PubMed1993

31P nuclear magnetic resonance studies on the glycogenolysis regulation in resting and contracting frog skeletal muscle.

1. Regulation of glycogenolysis in frog skeletal muscle at rest and following contraction was studied by measuring the concentration of phosphate-containing metabolites and the intracellular pH (pHi) in CN-treated muscles, in which oxidative phosphorylation was inhibited by NaCN, using the 31P nuclear magnetic resonance (NMR) technique. 2. When CN-treated muscles were kept at rest, the phosphocreatine (PCr) concentration very slowly decreased with time with a corresponding increase of the inorganic phosphate (Pi) concentration, while the ATP concentration remained unchanged. The pHi changed in the alkaline direction for the first 3 h, and then started to change in the acidic direction. 3. When CN-treated muscles were tetanized for 10 s, the PCr concentration decreased with a corresponding increase of the Pi concentration and acidification of pHi, while the ATP concentration remained unchanged. 4. When CN-treated muscles were tetanized repeatedly (each for 2 s) at constant intervals, the pHi changed in the alkaline direction following the first and the second tetani, and then changed in the acidic direction following the subsequent tetani, indicating that the consumed ATP is first replenished by the Lohmann reaction, while glycogenolysis starts only when the total amount of contractile activity exceeds a critical value. 5. Irrespective of whether CN-treated muscles were kept at rest or tetanized repeatedly, the Pi concentration increased to about 8 mM (mmol/kg wet muscle) when glycogenolysis started, suggesting that the onset of glycogenolysis in CN-treated muscles is regulated by the Pi concentration. 6. The 'internal' buffering power of muscle cytosol was estimated to be 35 mM H+/pH unit in anaerobic muscles and 25 mM H+/pH unit in CN- and iodoacetic acid (IAA)-treated muscles. The 'internal' buffering power contains a contribution due to flux of carbon dioxide and lactic acid across the cell membrane. Evidence indicated that lactic acid flux is small.

Animals↗
PubMed1993

Molecular mechanism of ATP-dependent actin-myosin interaction in muscle contraction.

Among a variety of energy transduction mechanisms in biological systems, the mechanism of chemo-mechanical energy conversion in muscle contraction has been studied most intensively. From the standpoint of muscle biochemistry, muscle contraction is essentially the actomyosin ATPase reaction in solution. From the standpoint of muscle physiology, on the other hand, muscle contraction is the relative sliding between the thick and thin filaments resulting from the attachment-detachment cycle between actin and myosin. Although the large gap between muscle physiology and muscle biochemistry is now being gradually eliminated by various new experimental techniques such as the flash photolysis of caged compounds and in vitro motility assay systems, there still remain a number of uncertainties concerning the molecular mechanism of actin-myosin interaction coupled with hydrolysis of ATP. As described in this article, attention of most investigators in this research field has been focused on the detection of myosin head rotation coupled with muscle force generation. Unfortunately, however, attempts to detect the myosin head rotation have not yet been successful, despite the efforts of many investigators with various techniques including X-ray diffraction, quick freezing, and use of various probes attached to the myosin head. It seems therefore possible that the mechanism of muscle contraction might be different from the mechanism which have been generally accepted. This possibility seems to be supported, for example, by the unexpected dissociation between the ATPase activity and the force development in muscle fibers treated with anti-S-2 antibody (Fig. 9C).

Actins↗
PubMed1993

Measurement of transverse stiffness during contraction in frog skeletal muscle using scanning laser acoustic microscope.

The change in the transverse propagation velocity was measured by the scanning laser acoustic microscope (SLAM) during contraction in living frog skeletal muscles. The images of the interferogram were processed by image-analyzer and the propagation velocity was calculated from the shift of the interference lines at rest and during contraction. In all the measurements, the velocities during contraction were clearly slower than at rest and this fact indicates that the transverse stiffness decreased during contraction. After stimulation, the beginning of the decrease in the propagation velocity preceded that of the increase in force by 30-40 ms, suggesting that the decrease in the transverse stiffness reflects the molecular mechanism of force development in muscular contraction.

Acoustics↗
PubMed1993

Scanning electron microscopy of the myosin-coated surface of polystyrene beads in a force-movement assay system for ATP-dependent actin-myosin sliding.

We examined the myosin-coated surface of polystyrene beads, which slide on actin filaments in the presence of ATP with characteristics essentially similar to those of contracting muscle, using a high-resolution scanning electron microscope (JSM-890, JEOL). The bead surface was mostly covered with myosin filaments (diameter, 15-45 nm) with helically arranged myosin heads. Considering the amount of force generated by the myosin heads on the bead (approximately 10 pN), this result indicates that the bead movement may be caused by about 10 myosin heads within a short myosin filament segment, but not by randomly oriented myosin heads.

Actins↗
PubMed1993

[Molecular mechanism of excitation and contraction in cardiac muscle].

The function of the heart is to pump blood in sufficient quantity to satisfy the metabolic requirements of tissues in the body at any given time. There are two ways by which the heart pumps different amounts of blood per unit time; one is the change in frequency of contraction, while the other is the amount of blood ejected during a single contraction (stroke volume). The former is related to the frequency of generation of action potential in the pacemaker cells, while the other is concerned with the change in myoplasmic Ca2+ concentration and the change in Ca(2+)-sensitivity of the contractile system. A number of regulatory mechanisms, with overlaps in their function, are involved in both cases.

Action Potentials↗
PubMed1993

Freeze-fracture studies on the cross-bridge angle distribution at various states and the thin filament stiffness in single skinned frog muscle fibers.

To give information about the changes of cross-bridge (myosin head) orientation during muscle contraction, mechanically skinned frog muscle fibers were rapidly frozen at various states, and the cross-bridges were observed on freeze-etch replicas. The number of cross-bridges per unit length of thick filament in relaxed state was less than one-third of that in contracting and rigor states. The interval between adjacent cross-bridges was maximum around 35 nm, a value close to the crossover repeat of actin helix. The cross-bridge angle distribution, as measured with a digital image processor, showed a peak around 90 degrees in all the states examined. The proportion of cross-bridges with angles around 90 degrees decreased either after stretch or after release of fibers in rigor state. The axial spacing of actin monomers in the thin filament was found to increase with increasing rigor force, to give the thin filament stiffness (times unit length) of about 1.8 x 10(4) pN. These results are discussed in connection with the mechanical properties of cross-bridges.

Actins↗
PubMed1993

Myofilament sliding per ATP molecule in rabbit muscle fibres studied using laser flash photolysis of caged ATP.

1. To estimate the distance of myofilament sliding per ATP molecule hydrolysed during the actin-myosin interaction in muscle, single glycerinated fibres prepared from rabbit psoas muscle were made to shorten under very small external loads (< or = 0.0005 maximum isometric force (Po), at 20-22 degrees C) by the laser flash photolysis of caged ATP (P3-1-(2-nitro) phenylethyladenosine 5'-triphosphate), a biologically inert and photolabile precursor of ATP. The laser flash-induced fibre shortening was recorded with a high-speed video system at 200 frames s-1. 2. Following the photochemical release of 75-300 microM ATP, the fibres shortened uniformly along the fibre length not only at the level of fibre segments but also at the level of sarcomeres. The fibres did not shorten appreciably in response to 50 microM ATP. 3. The initial velocity of the laser flash-induced fibre shortening increased with increasing concentration of released ATP, being 0.05 +/- 0.01, 0.12 +/- 0.04, 0.23 +/- 0.04, 0.38 +/- 0.03 and 0.95 +/- 0.08 microns s-1 (half-sarcomere)-1 (means +/- S.E.M., n = 10) with 75, 100, 150, 200 and 300 microM ATP, respectively. 4. The distance of the laser flash-induced fibre shortening also increased with increasing concentration of released ATP, being 10 +/- 2, 25 +/- 5, 65 +/- 7, 100 +/- 10 and 180 +/- 20 nm (half-sarcomere)-1 (means +/- S.E.M., n = 10) with 75, 100, 150, 200 and 300 microM ATP, respectively. 5. Comparison of the initial shortening velocities of the laser flash-induced shortening with the force-velocity relation of maximally Ca(2+)-activated fibres indicated the presence of considerable internal resistance against myofilament sliding following release of ATP. The initial velocity of shortening following the release of 300, 150 and 75 microM ATP was equal to the shortening velocity of maximally Ca(2+)-activated fibres under an external load of 0.55, 0.93 and 0.98 Po respectively. 6. These results suggest that, under nearly isometric conditions, the distance of myofilament sliding per ATP molecule hydrolysed is about 10 nm in each half-sarcomere.

Actin Cytoskeleton↗
PubMed1992

Contraction characteristics and ATPase activity of skeletal muscle fibers in the presence of antibody to myosin subfragment 2.

To investigate the role of the myosin hinge region in muscle contraction, we examined the contraction characteristics and Mg-ATPase activity of glycerinated muscle fibers prepared from rabbit psoas in the presence and absence of polyclonal antibody directed against the subfragment 2 (S-2) region of myosin. The antibody-induced reduction of Ca(2+)-activated isometric force was always accompanied by a parallel decrease of muscle fiber stiffness, so that the stiffness versus force relation remained unchanged by the antibody treatment. Force-velocity relations of the fibers, obtained by applying ramp decreases in force at steady isometric forces, indicated that the antibody had no effect on maximum shortening velocity or on the shape of force-velocity curves. Simultaneous measurements of Mg-ATPase activity and Ca(2+)-activated force showed that Mg-ATPase activity of the fibers remained unchanged despite the antibody-induced reduction of isometric force even to zero. These results indicate that when anti-S-2 antibody attaches to the S-2 region of myosin molecules, their heads still hydrolyze ATP but no longer contribute to both force generation and muscle fiber stiffness.

Animals↗
PubMed1992

Stretch-induced force development in Mytilus smooth muscle during submaximal activation.

When the anterior byssal retractor muscle of Mytilus edulis is stretched by 5-20% during submaximal activation with 100 mM K+ or 10(-5) M acetylcholine, it exhibited a delayed force development after the completion of stretch. The effect of ions and drugs on the stretch-induced activation suggests the stretch-induced release of Ca2+ from the inner surface of the plasma membrane.

Acetylcholine↗
PubMed1992

[A case of Legionella pneumonia with myelodysplastic syndrome].

A 40-year-old man was admitted with high fever and cough. Pneumonic shadows of the left middle and lower lung fields increased rapidly, and his blood gases worsened. Initial treatment with cefmenoxime, piperacillin, and minocycline was ineffective. Administration of rifampicin was started for suspected legionella pneumonia, but it did not control the spread of the pneumonia shadows. After addition of an antifungal agent and trimethoprim-sulfamethoxazole, his symptoms gradually improved. Isolation of Legionella pneumophila from sputum specimens collected on the 4th day of admission confirmed the diagnosis on day 10. The patient was then given oral rifampicin plus cefmenoxime to prevent mixed infection, and showed a satisfactory improvement. Legionella pneumonia developed secondary to compromise of the patient's immunity due to steroid therapy for MDS. After recovering from Legionella pneumonia, the patient subsequently developed tuberculous pleurisy and Pneumocystis carinii pneumonia, which were cured by antituberculous therapy and trimethoprim-sulfamethoxazole. However, acute hepatitis followed by hepatic failure developed, and he died on day 121 after admission.

Adult↗