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Biomedical subjects

H Mashima

Publications and source records attributed to H Mashima.

At least 55 records · Page 3Linked to original sources
PubMed1979

The dynamics of contraction in the guinea pig taenia coli.

Tension-length, load-velocity and tension-extension relations were studied in the taenia coli muscle of the guinea pig weighing 0.25--0.5 kg at 36--37 degrees C. The muscle was relaxed by 10(-6) g/ml adrenaline and stimulated by a strong AC field. The tension-length diagram was far wider than that of the skeletal muscle and sufficient tension was generated at longer lengths than 1.8 Lm, where Lm is the optimal length at which the maximum tension, Fm, is generated. The developed force per unit cross-sectional area was almost unchanged between 1.2--2.0 Lm. Average of the maximum forces was 2.2 kg/cm2. Load-velocity curves obtained at various isometric forces at Lm coincided with each other, if the velocity was plotted against the relative force. All curves can be expressed by a single force-load-velocity equation, (P+A)(v+b)=b(F+A), A=(F/Fm)a, where P is the load, F the isometric force, v the velocity, a and b are constants. The maximum velocity per unit muscle length was constant, irrespective of the muscle length. The compliance of the series elastic component, that is, the slope of the tension-extension curve, did not depend on the isometric force but decreased with decreasing muscle length. The internal lengthening of the series elastic component by the full isometric tension was about 3% of the muscle length at Lm.

Animals↗
PubMed1978

Binding of 45Ca to intercalated discs of cardiac muscles studied by electron microscope autoradiography.

The binding sites of Ca2+ entering the injured cardiac muscle cell was investigated by 45Ca electron microscope autoradiography in guinea pig papillary muscle and in frog ventricular muscle. The muscle was injured in Ca-free Tyrode's solution, transfered into 45Ca-Tyrode's solution and, after 30 min, fixed and cut into thin sections. An autoradiogram was taken after exposure (4--7 weeks) the thin film of the section was developed. Fine, or sometimes filamentous, silver grains produced by radiation with 45Ca were frequently observed on the intercalated discs of injured cells where most of the nexal membranes were separated. The number of 45Ca grains on the discs of injured cells was eight times more than that found on intact cells. The concentration of 45Ca grains estimated by the number of grains per unit area was 3.2 times higher in the disc region than that in the other cytoplasmic regions in the injured cells, while in the intact cells it was only 1/3 of that found in the latter. The localization of 45Ca grains along the disc of the injured cell was also examined and the fine grains were seen to be located on the separated nexal membrane or at the cytoplasmic side of the desmosome and fascia adherens. It is likely that Ca2+ binds with the nexal membrane and the resulting structural change, such as nexal separation, is indispensable for intercellular uncoupling or healing-over of cardiac muscles.

Animals↗
PubMed1977

Tetanic contraction and tension-length relation of frog ventricular muscle.

Complete tetanic contraction was generated in frog ventricular muscle by repetitive electrical stimulation. The maximum stimulus was a transverse alternating current at 10 Hz and 17-20 V/cm in peak to peak voltage in an external solution containing 9 mM Ca2+. The maximum isometric tension thus obtained was twice or more than that of the twitch tension at 20 degrees C. The tetanic tension and its rate of rise declined with decreasing external Ca2+ concentration and less than half of the maximum tension was generated at 1.8 mM Ca2+. Various tetanic tensions less than the maximum were obtained in the partially depolarized muscle in excess K+ solution by reducing the stimulus intensity. Adrenaline (5X10(-6)g/ml) potentiated the submaximal tetanic tension as well as the twitch tension, although no effect was observed for the maximum tetanic tension. The tension-length relation for the tetanic contraction of ventricular muscle was similar to that of the skeletal muscle, but the tension fell almost linearly at shorter lengths than 0.9 Lm, where Lm is the optimum length at which the maximum tension, Fm, was generated. Fm was 4.6 g/mm2, while the sarcomere length at Lm was 2.0-2.2 mum.

Animals↗
PubMed1977

Force-load-velocity relation and the internal load of tetanized frog cardiac muscle.

A frog ventricular muscle strip could be fully tetanized by alternating current stimulation at 10 Hz and 20 V/cm in a solution containing 9 mM Ca2+. During isometric tetanus, the controlled release was made and the shortening velocities against various loads were measured. The isometric force was varied by reducing the stimulus intensity in K+-rich solution, or by reducing the external Ca2+ concentration. The force-load-velocity relation was described by a simple hyperbolic equation: (P+A)(v+b)=b(F+A), A=(F/Fm)a for shortening, and (2F-P+A')(-v+b')=b'(F+A'),A'=(F/Fm)a' for lengthening, where F is the isometric force, Fm is the maximum isometric force at the optimal muscle length, Lm, P is the load, v is the velocity, a, b, a' and b' are constants. The values of constants were a/Fm=0.51, b=0.75 Lm/sec for shortening and a'/Fm=0.39, b'=0.75 Lm/sec for lengthening at 20 degrees C. At muscle lengths shorter than 0.92 Lm, the internal load defined as the difference between the external load and calculated load at a given velocity increased in proportion to both the velocity and the decrease in muscle length.

Animals↗
PubMed1976

Contraction produced by intracellular injection of calcium, strontium, and barium in the single crayfish muscle fibers.

Ca ions were ionophoretically injected through an intracellular microelectrode into the single muscle fiber of a crayfish, and the resulting contraction sphere was observed under a microscope and photographed with a movie camera. The minimum contraction produced by the threshold current involved usually three or four, sometimes two, sarcomers on both sides of the injecting pipette but contraction involving only one sarcomere was not observered. The rheobase of the Ca-injecting current was 3.2 X 10(-9) A. The strength-duration curves were determined for Ca-, Sr-, and Ba-injecting currents; all fitted a similar hyperbolic equation. The threshold amount of Ca above rheobasic injection was 2.1 X 10(-15)mol, and the ratios between threshold amounts were Ca: Sr: Ba=1: 1.9: 3.0. The effects of Ca and Sr were additive for the contraction. More current was required for the Ca-injection to produce the contraction in the K-depolarized-or 15mM-procaine-treated muscle, although less current was sufficient for the muscle treated with 0.5-1.0 mM of caffeine. The participation of the Ca-induced Ca release mechanism in the contraction produced by Ca injection and the role of Sr or Ba as a substitute for Ca were discussed.

Animals↗
PubMed1976

A mechanochemical model for the steady and transient contractions of the skeletal muscle.

A mechanochemical model for muscle contraction was presented which consisted of three subsystems: the regulatory mechanism of contraction by Ca ion, the cross-bridge cycle coupled with actin-myosin interaction and the dynamics of contraction with an external load. It was assumed that both the rate constant of the cross-bridge cycle and the net force of the cross-bridge were linear functions of the sliding velocity. Most parameters in the model were determined from the experimental data, but several were estimated by simulation techniques. The model adequately described the force-load-velocity relation, the rates of energy and heat output as well as some basic mechanical properties of muscle. Not only the steady-state contraction but also the twitch response could be explained by the model. Time courses of tension and shortening during isometric and isotonic twitches were calculated by the model on a digital computer. The calculated curves agreed satisfactorily with the experimental ones obtained from the frog semitendinosus muscle. The rate of tension rise of the isometric twitch was shown to attain the peak at nearly the same time as does the calculated Ca concentration curve.

Actins↗