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T Oba

Publications and source records attributed to T Oba.

At least 73 records · Page 4Linked to original sources
PubMed1981

Light diffraction studies of active muscles fibres as a function of sarcomere length.

This investigation has established the following points. (1) Activation of single intact frog muscle fibres or mechanically skinned fibres results in a decrease in the intensity of the first-order line at all sarcomere lengths at which filament overlap is present. (2) At long sarcomere lengths (greater than 3.6 micrometers) the intensity decrease upon stimulation of intact fibres diminishes until above 3.9 micrometers no decrease is seen. In the skinned preparation, no intensity change is seen at sacromere lengths above 3.6 micrometers. (3) The intensity decrease seen in the intact fibres in the 3.6-3.9 micrometers sarcomere length region may be due to contraction of sarcomeres near the tendons, which have a shorter sarcomere length than those illuminated by the laser beam, and thus may not be stretched beyond filament overlap. (4) No intensity decrease is observed upon activation at very long (greater than 4.5 micrometers) sarcomere lengths. (5) Mechanically skinned fibres show a graded intensity response to free calcium. (6) Scans of first-order line width show no broadening upon activation, indicating that sarcomere length dispersion in the illuminated region of the fibre does not increase.

Animals↗
PubMed1981

Intensity of light diffraction from striated muscle as a function of incident angle.

In a recently developed theory of light diffraction by single striated muscle fibers, we considered only the case of normal beam incidence. The present investigation represents both an experimental and theoretical extension of the previous work to arbitrary incident angle. Angle scan profiles over a 50 degrees range of incident angle (+25 degrees to -25 degrees) were obtained at different sarcomere lengths. Left and right first-order scan peak separations were found to be a function of sarcomere length (separation angle = 2 theta B), and good agreement was found between theory and experiment. Our theoretical analysis further showed that a myofibrillar population with a single common skew angle can yield an angle scan profile containing many peaks. Thus, it is not necessary to associate each peak with a different skew population. Finally, we have found that symmetry angle, theta s, also varies with sarcomere length, but not in a regular manner. Its value at a given sarcomere length is a function of a particular region of a given fiber and represents the average skew angle of all the myofibril populations illuminated. The intensity of a diffraction order line is considered to be principally the resultant of two interference phenomena. The first is a volume-grating phenomenon which results from the periodic A-I band structure of the fiber (with some contribution from Z bands and H zones). The second is Bragg reflection from skew planes, if the correct relation between incident angle and skew angle is met. This may result in intensity asymmetry between the left and right first order lines.

Animals↗
PubMed1981

Influence of temperature and external Ca2+ concentration upon dantrolene action on excitation-contraction coupling in frog skeletal muscle.

Effects of dantrolene (DAN) on electrical and mechanical responses in frog skeletal muscle were studied at various Ca2+ concentrations and temperatures to elucidate the mechanism of action of DAN. The following results were obtained. (a) Twitch tension of a DAN-injected fiber, elicited by intracellular stimulation, increased transiently and then decreased whereas extracellular DAN always depressed the tension. (b) Lowering the external Ca2+ concentration resulted in the potentiation of twitch tension. The addition of DAN, however, reduced the tension significantly (p less than 0.05). (c) Extracellular DAN caused a transient reduction and subsequent elevation of the threshold current; however intracellular DAN caused only elevation of threshold. (d) DAN prevented the slow depolarization of the membrane in low Ca2+ medium. (e) These effects of the drug were temperature dependent, the effect being more pronounced at higher temperatures. These findings suggest that DAN may manifest its effects by replacement of Ca2+ from its binding sites on the membrane and that this occupation of the Ca2+ sites by DAN is temperature dependent.

Animals↗
PubMed1980

Study on tubular transient current and mechanical activation in skeletal muscle of frog.

The relation between membrane current and mechanical activity during excitation of frog muscle fibers was studied using two-microelectrode voltage clamp technique. The current flow upon excitation of membrane consisted of transient initial inward and subsequent outwards currents which were carried by Na+ influx and K+ efflux respectively. Blocking of the outward K+ current by 3,4-diaminopyridine resulted in appearance of a late inward current associated with marked potentiation of twitch tension. Detubulation of the fiber by treatment with hypertonic glycerol suppressed the outward K+ current as well as the late inward current and abolished the contractile force. Dantrolene also gave similar effects on membrane currents and reduced twitch tension markedly. These results suggest that the late inward current through the T-system and not the outward K+ current may be the first step to lead the muscle cell to mechanical activation.

Animals↗
PubMed1978

Transient effect of intracellular dantrolene on E--C coupling in skeletal muscle.

The effect of dantrolene-Na (DAN) on electrical and mechanical responses was investigated to single fibers of frog semitendinosus. Twitch tension was potentiated over 2--4 min by intracellular application of DAN and was rapidly decreased thereafter. Extracellular DAN depressed the tension with all dosages used. Although DAN had no effect on membrane potential, it exerted a biphasic action on membrane excitability. From these results, a mechanism is postulated for the release of trigger Ca2+ from T-tubules.

Action Potentials↗