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M Hoshiyama

Publications and source records attributed to M Hoshiyama.

14 recordsLinked to original sources
PubMed1979

[Platelet factor 4].

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Blood Coagulation Factors↗
PubMed1976

Electrical and mechanical responses to diltiazem in potassium depolarized myocardium of the guinea pig.

Effects of diltiazem on the electrical and mechanical activities of guinea pig papillary muscle were investigated in K-rich Tyrode's solution (Kc1 12.7 mM). The electrical properties of cell membrane in K-rich solution were also examined in the ventricular muscle fibers. It was found that the overshoot as well as the maximum rate of rise (Vmax) of the action potential were highly sensitive to the extracellular concentration of CaC12 in K-rich solution. Vmax was also affected by NaC1. Diltiazem at a lower concentration (1.1 X 10(-7) M) caused a reduction in the contractile force of K-depolarized papillary muscle without producing significant changes in the resting and action potentials. In the presence of a higher concentration of diltiazem (1.1 X 10(-5) M), the contractile force decreased concurrently with the change in the action potential. Addition of CaC12 restored the original strength of contraction in parallel to the recovery of the action potential, especially in its overshoot and Vmax. From these results, it is inferred that diltiazem may decrease the contractile force of guinea pig papillary muscle either by interfering with the intrasmembrane calcium influx or by intracellularly reducing the free calcium ion concentration in the myoplasm.

Action Potentials↗
PubMed1975

Effect of diltiazem on electrical and mechanical activity of isolated cardiac ventricular muscle of guinea pig.

Diltiazem, a new 1,5-benzothiazepine derivative, antagonized calcium ion and thus caused a reduction in the contractile force of isolated papillary muscle. The antagonistic ratio of diltiazem to calcium ion was estimated to be approx. 1: 100. A lower concentration of diltiazem (2.2 x 10(-6) M) decreased the contractile force without affecting significantly the intracellularly recorded resting and action potentials. When the concentration of the compound was increased to 2.2 x 10(-5) M, only the maximum rate of rise of the action potential was reduced, while the other parameters of the action potential were also affected at 1.1 x 10(-4) M diltiazem. There was no significant change in the resting potential. Under conditions where the contractile force almost disappeared (1.1 x 10(-4) M), the membrane excitability was retained. It is concluded that diltiazem is an excitation-contraction uncoupler in the cardiac muscle cell and that the compound may exhibit its negative inotropic action by reducing in some way the intracellular concentration of free calcium ion available for the contractile mechanism.

Action Potentials↗