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H Sugi

Publications and source records attributed to H Sugi.

At least 55 records · Page 3Linked to original sources
PubMed1997

Stretch-induced enhancement of mechanical work production in frog single fibers and human muscle.

The relations between the velocity of prestretch and the mechanical energy liberated during the subsequent isovelocity release were studied in contractions of frog single fibers and human muscles. During isometric contractions of frog single fibers, a ramp stretch of varied velocity (amplitude, 0.02 fiber length; velocity, 0.08-1.0 fiber length/s) followed by a release (amplitude, 0.02 fiber length; velocity, 1.0 fiber length/s) was given, and the amount of work liberated during the release was measured. For human muscles, elbow flexions were performed with a prestretch of varied velocity (range, 40 degrees; velocity, 30-180 degrees/s) followed by an isokinetic shortening (velocity, 90 degrees/s). In both frog single fibers and human muscles, the work production increased with both the velocity of stretch and the peak of force attained before the release up to a certain level; thereafter it declined with the further increases of these variables. In human muscles, the enhancement of work production was not associated with a significant increase in integrated electromyogram. This suggests that changes in intrinsic mechanical properties of muscle fibers play an important role in the stretch-induced enhancement of work production.

Adult↗
PubMed1996

Effect of inorganic phosphate and ADP on the myofilament sliding induced by laser flash photolysis of caged ATP.

Using the technique of laser flash photolysis of caged ATP, we have suggested that, under nearly isometric conditions, the unitary distance of myofilament sliding per ATP molecule (myosin head powerstroke) is about 10 nm. To give further information about the mechanism of myofilament sliding, we studied the effect of inorganic phosphate (Pi) and ADP on the photoreleased ATP-induced shortening of single glycerinated muscle fibers under very small external loads. Both the velocity and the distance of the myofilament sliding induced by 150 microM ATP increased by Pi (20 mM), and decreased by ADP (0.4 mM). On the other hand, Pi and ADP showed no significant effect on the myofilament sliding induced by 100 and 75 microM ATP. The potentiating effect of Pi on the myofilament sliding with 150 microM ATP can be explained as being due to the increase in population of AM.ADP.Pi with corresponding decrease in population of AM.ADP, and also the increase in population of M.ADP.Pi and M.ATP. Meanwhile, the inhibitory effect of ADP can be simply accounted for to be due to an accumulation of AM.ADP that already finished their force generating process. The ineffectiveness of Pi and ADP on the myofilament sliding with 100 and 75 microM ATP is consistent with the view that it is caused by almost synchronized single myosin head powerstrokes.

Actin Cytoskeleton↗
PubMed1996

Different cardiac myosin isoforms exhibit equal force-generating ability in vitro.

We measured forces generated by myosin molecules and a single actin filament using an optical trap system. The force per unit length of actin filament did not differ significantly between cardiac myosin isoforms. V1 and V3. This indicates that the ability to generate force is equal between V1 and V3, despite their difference in the unloaded sliding velocity past actin.

Actins↗
PubMed1996

Nuclear magnetic resonance spectroscopy of skeletal muscle and muscle proteins.

NMR spectroscopy has widely been used as an important tool for the study of metabolism and the intracellular environment of various tissues. As the method is non-invasive, spectra can be recorded from living functioning tissues and their transient changes associated with activity analyzed. NMR is also a powerful technique to study the conformation of proteins and changes associated with their interaction with other molecules, which provide the structural basis for the physiological role of intracellular proteins. This review presents a brief theory of NMR and the applications of NMR to the physiological study of skeletal muscles, energy metabolism, intracellular environments including intracellular water and their changes with contraction. Also included is the application of NMR to the study of the conformation of muscle proteins, actin, myosin and Ca(2+)-binding proteins.

Animals↗
PubMed1995

Force-velocity relations of rat cardiac myosin isozymes sliding on algal cell actin cables in vitro.

The difference in kinetic properties between two myosin isozymes (V1 and V3) in rat ventricular myocardium was studied by determining the steady-state force-velocity (P-V) relations in the ATP-dependent movement of V1 and V3-coated polystyrene beads on actin cables of giant algal cells mounted on a centrifuge microscope. The maximum unloaded velocity of bead movement was larger for V1 than for V3. The velocity of bead movement decreased with increasing external load applied by the centrifuge microscope, and eventually reached zero when the load was equal to the maximum isometric force (P0) generated by the myosin heads. The maximum isometric force P0 was less than 10 pN, and did not differ significantly between V1 and V3. The P-V curves consisted of a hyperbolic part in the low force range and a non-hyperbolic part in the high force range. The critical force above which the curve deviated from the hyperbola was much smaller for V1 than for V3. An analysis using a model with an extremely small number of myosin heads involved in the bead movement suggested a marked difference in kinetic properties between V1 and V3.

Actins↗
PubMed1995

The force-velocity relationship of the ATP-dependent actin-myosin sliding causing cytoplasmic streaming in algal cells, studied using a centrifuge microscope.

When uncoated polystyrene beads suspended in Mg-ATP solution were introduced into the internodal cell of an alga Chara corallina, the beads moved along the actin cables with directions and velocities (30-62 microns s-1) similar to those of native cytoplasmic streaming. Bead movement was inhibited both in the absence of ATP and in the presence of CA2+, as with native cytoplasmic streaming. These results indicate that bead movement is caused by cytoplasmic myosin molecules attached to the head surface interacting with actin cables. The steady-state force-velocity relationship of the actin-myosin sliding that produces cytoplasmic streaming was determined by applying constant centrifugal forces to the beads moving on the actin cables. The force-velocity curve in the positive load region was nearly straight, and the implications of this shape are discussed in connection with the kinetic properties of the actin-myosin interaction in cytoplasmic streaming. It is suggested that the time for which a cytoplasmic myosin head is detached from actin in one cycle of actin-myosin interaction is very short. The Ca(2+)-induced actin-myosin linkages, responsible for the Ca(2+)-induced stoppage of cytoplasmic streaming, were shown to be much stronger than the rigor actin-myosin linkages.

Actins↗
PubMed1995

The mode of ATP-dependent microtubule-kinesin sliding in the auxotonic condition.

Kinesin is a motor protein that converts chemical energy derived from ATP hydrolysis into mechanical work to transport cellular components along microtubules. We studied the properties of ATP-dependent microtubule-kinesin sliding with two different in vitro assay systems. In one assay system, a kinesin-coated glass microneedle (elastic coefficient, 1-2.5 pN microns -1) was made to slide along an axoneme. Using this system, we obtained the relationship between the force (= load) on the microneedle and the velocity of microneedle-kinesin sliding in the auxotonic condition, in which the load on the microtubule-kinesin contacts increased as sliding progressed. The force-velocity curve was upwardly convex (maximum velocity Vmax, 0.58 +/- 0.15 microns s-1; maximum isometric force P0, 5.0 +/- 1.6 pN) and was similar to that of in vitro actin-myosin sliding in the auxotonic condition, suggesting that the two motor protein systems have fundamental kinetic properties in common. In the other assay system, an axoneme attached to a glass microneedle (elastic coefficient, 4-5 pN microns -1) was made to slide on a kinesin-coated glass surface (Vmax, 0.68 +/- 0.17 microns s-1; P0, 46.1 +/- 18.6 pN). The change in shape of the axoneme indicated an enormous flexibility of randomly oriented kinesin molecules.

Adenosine Triphosphate↗
PubMed1995

Synthesis and antipancreatitis activities of novel N-(2-sulfonylamino-5-trifluoromethyl-3-pyridyl)carboxamide derivatives as phospholipase A2 inhibitors.

Novel N-(2-sulfonylamino-5-trifluoromethyl-3-pyridyl)carboxamide derivatives have been prepared and evaluated as phospholipase A2 (PLA2) inhibitors. Among these compounds, IS-741 (sodium salt of 1j), which showed the highest and the most stable therapeutic effect on acute hemorrhagic pancreatitis induced by the closed duodenal loop method in rats, was selected as a candidate for further development.

Acute Disease↗
PubMed1995

Effect of lateral forces on the movement of myosin-coated beads on actin cables studied using a centrifuge microscope.

We developed an in vitro motility assay system, in which myosin-coated polystyrene beads were made to slide on actin filament arrays (actin cables) in giant algal cells and subjected to centrifugal forces, which were parallel to the direction of bead movement to serve as external loads on actin-myosin sliding (Oiwa et al. (1990) Proc Natl Acad Sci USA 87: 7893-7897), and succeeded in determining the steady-state force-velocity relation of ATP-dependent actin-myosin sliding. To give further information about the properties of actin-myosin sliding, we have applied centrifugal forces, in parallel with the plane of actin-myosin sliding but at right angles with the direction of bead movement, and have found that such "lateral" centrifugal forces reduced the velocity of bead movement. In addition, we have also found that the velocity of bead movement is reduced more markedly with lateral forces applied from the left side of the bead ("left" lateral forces) than those applied from the right side of the bead ("right" lateral forces). These results are discussed in connection with the direction of sliding force generated by the myosin heads on the bead which interact with the right-handed double helix of actin monomers constituting actin filaments.

Actins↗
PubMed1994

In vitro ATP-dependent F-actin sliding on myosin is not influenced by substitution or removal of bound nucleotide.

To examine possible role of F-actin-bound nucleotide in ATP-dependent actin-myosin sliding, we prepared various actin filaments with different nucleotide contents and compared their sliding velocities on heavy mero-myosin in the presence of 2'-deoxyadenosine 5'-triphosphate (dATP) to exclude possible exchange of external ATP with the actin-bound nucleotide. Neither the sliding velocity nor the length of the actin filaments was significantly influenced by substitution or removal of actin-bound nucleotide, indicating that actin-bound nucleotide may not play a significant role in the sliding between actin and myosin.

Actins↗
PubMed1994

EFFECT OF MECHANICAL VIBRATION ON ACTIVE TENSION IN THE LONGITUDINAL RETRACTOR MUSCLE OF A SEA CUCUMBER STICHOPUS JAPONICUS

1. The effect of mechanical vibration on active tension in an echinoderm somatic smooth muscle was studied using the longitudinal retractor muscle (LRM) of a sea cucumber Stichopus japonicus. 2. The steady contracture tension in LRM fibres maximally activated with 10(-3) mol l-1 acetylcholine (ACh) was reduced by vibrations (peak-to-peak amplitude, 0.5­2.5 % of l0, where l0 is the slack length of the muscle; frequency, 5­100 Hz). The extent of reduction of active contracture tension increased with increasing amplitude of vibration, but it did not change appreciably with increasing frequency of vibration. 3. The steady contracture tension in LRM fibres submaximally activated with 10(-5) mol l-1 ACh was more markedly reduced by vibrations than was that in maximally activated fibres. 4. The vibration-induced reduction of active contracture tension disappeared when temperature was lowered from 20­23 to 0 °C. 5. The development of contracture tension in LRM fibres activated with ACh was not affected by mechanical vibration. 6. These results are discussed in connection with the vibration-induced decrease in the rate of breakage of the actin­myosin linkages responsible for isometric force generation.

Journal Article↗
PubMed1994

Ultrastructural changes in glycerol-extracted skeletal muscle fibers after chemical modification of myosin heads with p-phenylenedimaleimide.

We examined the structural changes in relaxed glycerinated rabbit psoas muscle fibers induced by modification of the myosin heads with p-phenylenedimaleimide (p-PDM), which reacts with sulfhydryls on the myosin head to cause its loss of ability to combine with actin and to hydrolyse ATP. In the longitudinal sections of both chemically fixed and quickly frozen muscle fibers, ladder-like structures, interpreted as the myosin heads extending nearly at right angles with the thick filaments, were more prominent in the p-PDM-modified fibers than in the control fibers. Fourier transform diffractograms of the longitudinal sections exhibited a distinct 14.3-nm meridional reflection, which arises from axial spacing of the myosin heads on the thick filament, in the p-PDM-modified fibers, but not in the control fibers. These results indicate that the p-PDM-modification of the myosin heads causes an increase in the regularity of myosin head arrangement on the thick filament.

Animals↗
PubMed1993

Purification and characterization of a Ca(2+)-binding 450-kDa protein (MCBP-450) in the plasma membrane-enriched fraction from a molluscan smooth muscle.

In accordance with physiological and electronmicroscopic evidence that, in the anterior byssal retractor muscle (ABRM) of a common mussel Mytilus edulis, Ca2+ activating the contractile system is accumulated at the inner surface of the plasma membrane and at the membrane of sarcoplasmic reticulum (Ebashi, S. and Endo, M. (1968) Prog. Biophys. Mol. Biol. 18., 123-183; Suzuki, S. and Sugi, H. (1982) in The role of calcium in biological systems, Vol. I (Anghileri, L.J. and Tuffet-Anghileri, A.M., eds.), pp. 201-207, CRC Press, Boca Raton), we have found a high-molecular-mass (450 kDa) Ca(2+)-binding protein (MCBP-450) in the membrane fractions of the ABRM by 45Ca autoradiography of proteins transferred to nitrocellulose membrane (Rüegg, J. C. (1971) Physiol. Rev. 51, 201-248). MCBP-450, purified to electrophoretic homogeneity, exhibited Ca(2+)-dependent changes in mobility, tryptophan fluorescence, UV absorption and CD spectrum, indicating its Ca(2+)-dependent conformational changes. MCBP-450 has a high content of aspartic and glutamic acid (23.8%) and a high content of basic residues (27%). It has a high capacity Ca(2+)-binding site, which binds about 38 mol of Ca2+ per mol with an adissociation constant of 10(4) M-1, and a low-capacity Ca(2+)-binding site, which binds about 7 mol of Ca2+ per mol with an association constant of 10(5) M-1. These characteristics of MCBP-450 are consistent with the view that it is actually involved in regulating the contraction-relaxation cycle in the ABRM.

Amino Acids↗
PubMed1993

Dependence of the work done by ATP-induced actin-myosin sliding on the initial baseline force: its implications for kinetic properties of myosin heads in muscle contraction.

The properties of the ATP-dependent actin-myosin sliding responsible for muscle contraction was studied using an in vitro force-movement assay system, in which a myosin-coated glass microneedle was made to slide on actin filament arrays (actin cables) in the giant algal cell with iontophoretic application of ATP. With a constant amount of ATP application, the amount of work done by the actin-myosin sliding increased with increasing baseline force from zero to 0.4-0.6 Po, and then decreased with further increasing baseline force, thus giving a bell-shaped work versus baseline force relation. The result that the maximum actin-myosin sliding velocity did not change appreciably with increasing baseline force up to 0.4-0.6 Po implies, together with the limited number of myosin heads involved, that (1) the rate of power output of actin-myosin sliding is determined primarily by the amount of external load rather than the velocity of actin-myosin sliding, and (2) the bell shaped work versus baseline force relation (and also the hyperbolic force-velocity relation) results from the kinetic properties of individual myosin head rather than the change in the number of myosin heads involved.

Actins↗
PubMed1993

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

We studied the unitary distance of ATP-induced actin-myosin sliding using an in vitro force-movement assay system consisting of a myosin-coated glass microneedle and well organized actin filament arrays (actin cables) in the internodal cell of an alga Nitellopsis obtusa. The number of myosin heads interacting with actin cables was reduced to about 100, as judged from the isometric force of about 100 pN attained in the presence of 2 mM ATP. When the amount of iontophoretically applied ATP was reduced by decreasing the amount of charge passed through the ATP electrode from 80 to 2 nC, the distance of the ATP-induced actin-myosin sliding decreased almost linearly from about 100 to about 10 nm, no detectable sliding being observed with further reduction of charge through the electrode. The sliding distances with small amounts of ATP (7-16 nC) distributed around integral multiples of 10 nm, suggesting the unitary distance of actin-myosin sliding of about 10 nm.

Actins↗
PubMed1993

Kinetic properties of the ATP-dependent actin-myosin sliding as revealed by the force-movement assay system with a centrifuge microscope.

To study the kinetic properties of the ATP-dependent actin-myosin sliding responsible for muscle contraction, we developed an in vitro force-movement assay system, in which centrifugal forces were applied to myosin-coated polystyrene beads sliding along actin cables of giant algal cells in the presence of ATP. Under constant centrifugal forces directed opposite to the bead movement ("positive" loads), the beads moved with constant velocities. The steady-state force-velocity (P-V) curve thus obtained was double-hyperbolic in shape, being analogous to the P-V curve of single muscle fibers. Under constant centrifugal forces in the direction of the bead movement ("negative" loads), on the other hand, the beads also moved with constant velocities. Unexpectedly, the velocity of bead movement did not increase with increasing negative loads, but decreased markedly (by 20-60%). We also studied the effect of centrifugal forces at right angles with actin cables on the bead movement.

Actins↗
PubMed1993

Distance of myofilament sliding per ATP molecule in skeletal muscle fibers studied using laser flash photolysis of caged ATP.

We studied the distance of myofilament sliding per hydrolysis of one ATP molecule by recording shortening of single glycerinated muscle fibers induced by laser flash photolysis of caged ATP, diffusion of photochemically released ATP out of the fiber being prevented by surrounding the fiber with silicone oil. With 75 microM ATP released (one half of the total myosin head concentration within the fiber), the fiber showed the minimum shortening (10 +/- 2 nm/half sarcomere, n = 10) taking place uniformly in each sarcomere in the fiber. Comparison of the initial flash-induced shortening velocity with the force-velocity relation of maximally Ca(2+)-activated fibers indicated that the above minimum fiber shortening took place under an internal load nearly equal to Po. These results may be taken to indicate that, under a nearly isometric condition, the distance of myofilament sliding per hydrolysis of one ATP molecule is of the order of 10 nm.

Actin Cytoskeleton↗