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M Takauji

Publications and source records attributed to M Takauji.

6 recordsLinked to original sources
PubMed1979

Biphasic time course of inactivation of potassium contractures in single twitch muscle fibers of the frog.

The time course of the inhibition of peak tension (inactivation) of potassium contracture induced by conditioning depolarization with 10, 15, 20 and 30 mM K+ was examined, using single twitch fibers from the frog semitendinosus muscle. The time-dependence curve of the inactivation was biphasic, consisting of the first phase and the second phase. The first phase was characterized as follows: 1) the time course and the extent depend on the degree of conditioning depolarization; 2) the inactivation proceeds exponentially and finally reaches a steady level; and 3) the rate is markedly increased by lowering Ca2+ in the external medium. It could be considered that the first phase of the inactivation is an analogical phenomenon with the inactivation of sodium conductance in a squid giant axon. The second phase of the inactivation induced by conditioning with 20 and 30 mM K+ reached its full inactivation independently of the degree of conditioning depolarization. On the basis of these results, the terms inactivation 1 and inactivation 2 were given to the first phase and second phase, respectively, of the time-dependence curve of the inactivation of potassium contracture.

Animals↗
PubMed1977

Inhibitory action of dantrolene sodium on the activation of excitation-contraction coupling in frog skeletal muscle.

Effect of dantrolene sodium on the activation of potassium contracture in single fibers of frog semitendinosus muscle was studied. Dantrolene shifted the activation curve to the right without changing the depolarization produced by a given K+ concentration. The shift of mechanical threshold by dantrolene was dependent on the concentration of calcium in the medium and the effects of dantrolene and Ca++ are additive to each other. On the other hand, the action of dantrolene is antagonized by Ca++ with respect to the peak tension in 190 mM K+. In addition, dantrolene did not release 45Ca from the self-exchangeable Ca fraction and did not affect the exchange of 45Ca in the self-exchangeable Ca fraction with 40Ca. It was also observed that dantrolene had no appreciable influence on the ultrastructure of muscle fibers under our experimental conditions. On the basis of these results, the mechanism of action of dantrolene on the activation of excitation-contraction coupling, the relation between the drug and calcium actions and the drug effect on the Ca movement in T-system membranes were discussed.

Animals↗
PubMed1976

Effect of Ca++ on Vmax measured in absence of external or internal load.

Myofibrils 1 sarcomere wide (single myofibrils) were prepared from rat heart. Mean initial sarcomere length was 2.68 mu. Contraction was initiated with 20, 25 or 100 muM MgATP and terminated with EGTA and EDTA. Single fibrils shortened at the theoretical Vmax for the in vitro conditions until sarcomere length reached 2.05 mu. At this length they encountered a significant internal afterload. Reaction time, substrate, and temperature were adjusted so that final sarcomere length was greater than or equal to 2.05 mu in most experiments. Ca++ increased Vmax of single fibrils 2- 4-fold. Results were similar at 20 and 100 muM MgATP, and in reaction mixture containing 100 or 140 mM KCI. We conclude that Ca++ controls not only the number of cross-bridges, but also the rate at which the cross-bridges turn over.

Animals↗
PubMed1975

Effect of dantrolene sodium on excitation-contraction coupling in frog skeletal muscle.

The effect of dantrolene sodium, 1-(5-(p-nitrophenyl)furfuryli-deneamino)hydantoin sodium hydrate, on electrical and mechanical response in frog skeltal muscles (whole muscles or single fibers) and on the biochemical properties of contractile proteins and fragmented sarcoplasmic reticulum isolated from frog or rabbit skeletal muscle was investigated. The peak tensions of twitch, tetanus and potassium contracture were significantly inhibited by dantrolene, without affecting the magnitude of resting potential, the amplitude and duration of action potential and the negative afterpotential. On the other hand, ATP-INDUCED SHORTENING OF GLYCEROL-EXTRACTED RABBIT PSOAS MUSCLE FIBERS, ATPase activity of frog myofibrils and Ca release induced by caffeine, Ca uptake and ATPase activity of fragmented sarcoplasmic reticulum of frog or rabbit muscle were not affected by dantrolene. Caffeine contracture was partially inhibited by dantrolene and was almost unchanged by it in potassium-depolarized muscele fiber. Nitrate ions and low concentration of caffeine rapidly recovered the twitch inhibition induced by dantrolene. These results suggested that dantrolene acts on the membrane of transverse tubules and possibly the triadic junction and that it inhibits the inward movement of Ca and subsequently decreases the release of activator Ca from sarcoplasmic reticulum.

Action Potentials↗
PubMedDate not supplied

Actin like filaments in the peritubular cells of human testis chemical extraction and binding with heavy meromyosin.

Two types of the cytoplasmic filaments are found in human peritubular cells; thin filaments (50-80 A) and 100 A filaments. The thin filaments are numerous and tightly packed in cytoplasma of peripheral cell processes, and form bundles. These bundles are arranged in parallel with the long axis of the cells. Dense areas are occasionally seen among the filaments, or underneath the cell membrane to which the thin filaments seem to be anchored. The 100 A filaments are generally located around the perinuclear region or in the middle region of cytoplasma. The thin filaments are not altered after incubation with Hasselbach-Schneider's solution. These filaments, however, disappear in cytoplasma when extracted with 0.6 M KI solution. And also, the thin filaments form chracteristic arrowhead complexes, when incubated with HMM, while these complexes are never found, when incubated with HMM plus ATP. The 100 A filaments do not react to HMM. Thus it is suggested that the thin filaments are actin or actin like and that a contractile system exists in human peritubular cells, which may be involved in transport of nonmotile sperm or permeability of the seminiferous walls.

Adult↗