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Biomedical subjects

H Sugi

Publications and source records attributed to H Sugi.

At least 145 records · Page 8Linked to original sources
PubMed1981

Isotonic velocity transients in frog muscle fibres following quick changes in load.

1. The isotonic velocity transients following quick changes in load were studied on tetanized frog skeletal muscle fibres with special reference to those following quick increases in load. 2. When the load was increased quickly from the maximum isometric force P0 to 1.05-1.3 P0, the fibres exhibited markedly oscillatory length changes with distinct reversal in the direction of movement before starting to lengthen with a nearly constant velocity. 3. The period of the oscillatory length changes increased with increasing magnitude of the load step, and decreased with increasing temperature. The amplitude of oscillatory length changes never exceeded 0.5% of the slack length L0, i.e. about 50 A per half-sarcomere. 4. If the load was increased quickly from P0 to 1.3-1.6 P0, the fibres lengthened continuously with velocities decreasing with time. 5. The response of fibres, shortening isotonically under a large load (about 0.8 P0), to quick increases in load was qualitatively similar to that of isometrically contracting fibres. 6. When quick increases in load were applied during isotonic shortening under a moderate or small load (0.1-0.6 P0), the fibres showed initial transient lengthening before starting to shorten against a new load, indicating a decrease in the ability of the fibres to sustain a load after a period of isotonic shortening and its restoration during the transient lengthening. 7. The extent of decrease in load-sustaining ability as well as its subsequent restoration process was dependent on both the amount of load and the duration of preceding isotonic shortening. 8. The decrease in the load-sustaining ability during the course of isotonic shortening appeared to be complete within 30-50 msec after the beginning of shortening. 9. These results are discussed in relation to the kinetic properties of the crossbridges responsible for muscle contraction.

Animals↗
PubMed1981

Enhancement of mechanical performance in frog muscle fibres after quick increases in load.

1. The change in the ability of frog skeletal muscle fibres to sustain a load was studied during the course of oscillatory length changes or continuous isotonic lengthening following quick increases in load, by applying "test' load steps and measuring the initial velocity of resulting isotonic motion. 2. When quick decreases in load were applied during oscillatory length changes or continuous isotonic lengthening, the fibres were found to shorten against a load above the maximum tension (P0), indicating an increase in load-sustaining ability after quick increases in load. 3. If quick increases in load were applied at various times after preceding quick increase in load, the initial velocity of resulting isotonic lengthening decreased with time, also indicating an increase in load-sustaining ability. 4. An increase in load-sustaining ability was also observed during the course of rapid isotonic lengthening under a load of 1.6-1.7 P0, in which the fibres lengthened with increasing velocity. 5. The increase in load-sustaining ability after quick increases in load was associated with a shift of the force-velocity curve towards higher force values, while no significant change was observed in the maximum shortening velocity at zero load. 6. The stiffness of muscle fibres was estimated by measuring quick length changes coincident with load steps. It decreased with decreasing isotonic load below P0, approaching a certain finite value as the load tended to zero. For isotonic load below P0, approaching a certain finite value as the load tended to zero. For isotonic loads above P0, the stiffness increased with increasing isotonic load up to 1.6-1.7 P0, when step decreases in load were used for stiffness measurements. 7. The mechanism of enhancement of mechanical performance of the fibres after quick increases in load is discussed in relation to the sliding filament/cross bridge hypotheses of muscle contraction.

Animals↗
PubMed1981

Rubeomycin, a new anthracycline antibiotic complex. I. Taxonomy of producing organism, isolation, characterization and biological activities of rubeomycin A, A1, B and B1.

A new antibiotic complex has been obtained from the cultures of an actinomycete, strain FA-1180, isolated from a soil sample collected at lake side of Biwa in Japan. On the basis of taxonomic studies the producing microorganism is designated as Actinomadura roseoviolacea var. biwakoensis nov. var. The antibiotic complex belongs to the class of anthracycline glycoside antibiotics. All components form deep red fine needles on crystallization; components are named rubeomycin A, A1, B and B1. These components exhibit activity against Gram-positive bacteria as well as Yoshida sarcoma cell in vitro. These components are also effective on P388 leukemia.

Animals↗
PubMed1980

Studies on the synthesis of chemotherapeutics. 10. Synthesis and antitumor activity of N-acyl- and N-(alkoxycarbonyl)-5-fluorouracil derivatives.

A number of N-acyl and N-(alkoxycarbonyl)-5-fluorouracil derivatives possessing, for example, benzoyl, o-toluyl, acetyl, propionyl, heptanoyl, ethoxycarbonyl, phenoxycarbonyl, and benzyloxycarbonyl groups as N1 and/or N3 substituents were synthesized, and their antitumor activities were evaluated. The synthesis was achieved by a direct and two-step acylation of 5-fluorouracil and by selective N1-deacetylation of N1-acetyl-N3-substituted-5-fluorouracil under appropriate reaction conditions. Several N3-benzoyl- and N3-o-toluyl-5-fluorouracil derivates and showed significant activity against experimental tumor, and N1-acetyl-N3-o-toluyl-5-fluorouracil was found to be most promising among them. Further investigation revealed 12 to retain higher activity toward various tumors, with lower toxicity and good blood level, than either 1 or FT-207, even for oral administration.

Animals↗
PubMed1980

Measurement of heat production during the summation of isometric contraction in frog skeletal muscle with an infrared radiometer.

The heat production of frog skeletal muscle during isometric contraction was measured with an infrared radiometer at room temperature (23--26 degrees C), attention being focused on the heat produced during the summation of twitches by two successive stimuli. When the amount of heat produced by the second stimulus was plotted against the corresponding tension increment, the data points fell on two regression lines of approximately the same slope except for the intermediate stimulus intervals. One regression line started from the origin, while the other intersected the ordinate at about 1 mcal/g. If a twitch was produced at various times after a 0.5 sec tetanus, all the data points on the heat versus tension increment plot distributed around a single regression line starting from the origin. These results are explained by assuming that the relation between the tension-dependent heat and the tension increment in a twitch produced after a preceding mechanical response remains nearly constant irrespective of the stimulus interval, while the amount of tension-independent heat production varies depending on the time after the preceding stimulation.

Animals↗
PubMed1979

The origin of the series elastic component in single crayfish muscle fibres.

High-speed cinematographic studies on the length changes of single tetanized crayfish muscle fibres during a step decrease in length revealed a farily uniform distribution of a highly compliant series elastic component along the fibre length, suggesting that it mainly originates from some structures in each sarcomere other than the cross-bridges.

Animals↗
PubMed1979

The origin of the instantaneous elasticity in single frog muscle fibres.

High-speed cinematographic recordings of single tetanized muscle fibres during a quick decrease in length revealed that the shortening was mostly localized at the fibre segment nearest the released end of the fibre, indicating that the instantaneous elasticity may not originate from the elasticity of the cross-bridges.

Animals↗
PubMed1979

The effect of sarcomere length and stretching on the rate of ATP splitting in glycerinated rabbit psoas muscle fibers.

The effect of sarcomere length and stretching on the tension and the rate of ATP splitting was studied using small fiber bundles from glycerinated rabbit psoas muscle. The rate of ATP slitting was determined by measuring ADP production, while the tension development in response to a contracting solution (at pCa 5.3) was recorded in the same preparation. The isometric tension developed by the preparation decreased when the sarcomere length was increased. The decrease of tension development was accompanied by a decrease in the rate of ATP splitting. If a preparation exerting steady isometric tension was stretched by 5--10% at a velocity of 0.1 mm/s, the rate of ATP splitting was increased after stretching, while the steady isometric tension attained after stretching was also higher than the initial value. The extent of the excess ATP splitting caused by stretching decreased with increasing sarcomere length. These results suggest that the rate of the interaction cycle between actin and myosin molecules may increase as a result of stretching.

Adenosine Triphosphatases↗
PubMed1979

The change in the load-sustaining ability and in the series elasticity in Mytilus smooth muscle during isotonic shortening.

1. The change in the ability to sustain a load and the change in the series elasticity in the anterior byssal retractor muscle (a.b.r.m.) of Mytilus edulis during isotonic shortening was studied by recording the length changes following step changes in load. 2. When a load of 0.7--0.9 P0 WAs applied after a period of isotonic shortening under a small load (0.05--0.1 P0), the muscle fibres showed continuous isotonic lengthening, indicating a reduction in the ability to sustain a load during isotonic shortening. 3. Following the application of a load of 0.3--0.6 P0 during isotonic shortening under a small load, the fibres exhibited a transient isotonic lengthening before starting to shorten isotonically, indicating some degree of restoration in the load-sustaining ability after the step increase in load. 4. No appreciable reduction in the load-sustaining ability was observed during isotonic shortening under a large load (more than 0.7 P0). 5. The load--extension curves of the series elasticity determined during isotonic shortening were found to be scaled down roughly in proportion to the isotonic load. 6. The stiffness of the muscle fibres during the isotonic shortening approached a certain finite value, when the isotonic load tended to zero. If the stiffness was measured during the development of isometric tension, the stiffness--isometric tension curve extrapolated towards the origin. 7. High-speed cinematography during the step change in load indicated a fairly uniform distribution of the series elasticity along the length of the preparation. 8. These results are discussed in relation to the sliding filament model of muscle contraction.

Animals↗
PubMed1978

Ultrastructural and physiological studies on the longitudinal body wall muscle of Dolabella auricularia. I. Mechanical response and ultrastructure.

The physiological properties of mechanical response and the ultrastructure in the longitudinal body wall muscle (LBWM) of the opisthobranch mollusc Dolabella auricularia were studied to obtain information about excitation-contraction coupling in somatic smooth muscles responsible for smooth and slow body movement of molluscans. The contracture tension produced by 400 mM K was not affected by Mn ions (5--10 mM) and low pH (up to 4.0), but was reduced by procaine (2 mM). The K-contracture tension was not readily eliminated in a Ca-free solution containing ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA). A large contracture tension was also produced by rapid cooling of the surrounding fluid from 20 degrees to 5 degrees--3 degrees C even when the preparation showed no mechanical response to 400 mM K after prolonged (more than 2 h) soaking in the Ca-free solution. These results indicate that the LBWM fibers contain a large amount of intracellularly stored Ca which can be effectively released by membrane depolarization. The fibers were connected with each other, forming the gap junctions, the desmosomes, and the intermediate junctions. The sarcoplasmic reticulum (SR) consisted of vesicular and tubular elements, and was mostly located near the fiber surface. The plasma membrane showed marked tubular invaginations of 600-800 A in diameter, with many branches (surface tubules), extending inwards for approximately 2 micron. These surface tubules were closely apposed to the SR, and the bridgelike structures analogous to those in the triadic junction of vertebrate skeletal muscle were observed in the space between the surface tubules and the SR. It is suggested that the influence of membrane depolarization is transmitted inwards along the surface tubules to cause the release of Ca from the SR.

Acetylcholine↗
PubMed1978

Ultrastructural and physiological studies on the longitudinal body wall muscle of Dolabella auricularia. II. Localization of intracellular calcium and its translocation during mechanical activity.

The localization of Ca-accumulating structures in the longitudinal body wall muscle (LBWM) of the opisthobranch mollusc Dolabella auricularia and their role in the contraction-relaxation cycle were studied by fixing the LBWM fibers at rest and during mechanical response to 400 mM K or to 10(-4)--10(-3) M acetylcholine in a 1% OsO4 solution containing 2% K pyroantimonate. In the resting fibers, electron-opaque pyroantimonate precipitate was mostly localized at the peripheral structures, i.e., along the inner surface of the plasma membrane, at the membrane of the surface tubules, and at the sarcoplasmic reticulum. In the fibers fixed during mechanical activity, 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. Electron-probe X-ray microanalysis showed the presence of Ca in the precipitate, indicating that the precipitate may serve as a measure of Ca localization. These results are in accord with the view that, in the LBWM, the Ca stored in the peripheral structures is released into the myoplasm to activate the contractile mechanism.

Animals↗