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Biomedical subjects

H Imamura

Publications and source records attributed to H Imamura.

At least 415 records · Page 23Linked to original sources
PubMed1976

Restoration by histamine of the calcium-dependent electrical and mechanical response in the guinea-pig papillary muscle partially depolarized by potassium.

Electrophysiological and mechanical effects of histamine were observed in guinea-pig papillary muscle which had been depolarized and rendered inexcitable by elevation of potassium concentration in Tyrode solution to 27 mM. 1. Histamine (3 X 10(-7) to 3 X 10(-5) M) restored the action potential and tension development. The amplitude of the action potential was increased by 31.6 mV/10-fold increase in extracellular Ca2+ concentration. Nifedipine (10(-6) M) abolished the electrical and mechanical responses which had been restored by histamine (10(-5) M) but TTX (10(-5) M) did not affect them. Reduction of the extracellular Na+ concentration to one half decreased the amplitude and the maximum rate of rise of the action potential restored by histamine (10(-5) M) while the peak tension was increased and an after-contraction occurred. 2. The maximum rate of rise and the amplitude of the action potential restored by histamine (10(-5) M) decreased with increase in stimulus frequency from 0.1-1.6 Hz. The peak tension decreased and then increased. The shape of the developed tension was also changed. In the presence of caffeine (1 mM), the only effect of an increase in stimulus frequency was a decrease in peak tension but the change in the shape of developed tension did not occur. 3. The electrical and mechanical responses restored by histamine (3 X 10(-6) or 10(-5) M) were depressed by metiamide (3 X 10(-6) M) but not by diphenhydramine (10(-5) M) or bufetolol (10(-6) M). 4. The electrical response restored by histamine (10(-6) or 10(-5) M) was enhanced by papaverine (10(-5) M) and depressed by N-methylimidazole (10 mM). It is concluded that histamine may enhance the slow inward Ca2+ current mediated by histamine H2-receptors and the adenylate cyclase system in ventricular muscle and that the positive inotropic action of histamine may be attributed to these mechanisms.

Action Potentials↗
PubMed1976

[Pharmacological studies of 2-(5H-[1]benzopyrano[2,3-b]pyridin-7-yl) propionic acid (Y-8004) (II). General pharmacological action].

This anti-inflammatory agent proved to have a therapeutic margin wider than that of indomethacin. Y-8004 exhibited little effect on the central nervous system, somatic and autonomic nervous system. On the cardiovascular system in dogs, Y-8004 induced a slight transient fall in blood pressure followed by a pressor response, increase in heart rate and coronary vasodilation at a dose of 30 mg/kg given intravenously, but no remarkable change was seen on the electrocardiogram. Y-8004 showed no effect on isolated smooth muscles such as vas deferens, ileum and atria, but inhibited gastrointestinal propulsion at a dose of 100 mg/kg given orally in mice and spontaneous contractions of the pregnant uterus of rats at a concentration of more than 10(-6)M. This agent also decreased urine volume and electrolytes in rats. This property was considered to be common to other acidic nonsteroidal anti-inflammatory agents. On the other hand, in guinea pigs, Y-8004 inhibited the bradykinin-induced bronchoconstriction and the collagen-induced platelet aggregation to a greater extent than did indomethacin. These findings suggest that Y-8004 is an active compound with properties similar to acidic non-steroidal anti-inflammatory agents such as indomethacin.

Animals↗
PubMed1976

Effects of bufetolol and propranolol on active and passive membrane properties of dog papillary muscle.

Effects of bufetolol and propranolol, adrenergic beta-receptor blocking and anti-arrhythmic drugs, on active and passive membrane properties of the dog papillary muscle were investigated with microelectrode and sucrose-gap methods. Bufetolol (10(-5) to 10(-4) g/ml) and propranolol (10(-6) g/ml) significantly decreased the maximum rate of rise of the action potential. The maximum responsive frequency to driving stimulus was decreased in the presence of bufetolol (3 X 10(-5) g/ml) and propranolol (10(-5 g/ml), whereas the effective refractory period was not affected. The critical threshold potential was shifted to more positive potential in the presence of the drugs. The passive membrane property, the space constant (lambda), the time constant (tau) and the current-voltage relations of the muscle membrane were not significantly altered by the drugs. It is concluded that bufetolol and propranolol suppress the excitability of the muscle membrane and this action may be ascribed to the decrease in the sodium conductance (gNa) and to the rise of gNa onset potential without alteration in the passive membrane property.

Action Potentials↗
PubMed1976

[Antibacterial and bactericidal activity of tinidazole against anaerobic bacteria comparing with metronidazole (author's transl)].

Antibacterial activity of tinidazole (1-2-(ethylsulfonyl)-2-methyl-5-nitroimidazole) against anaerobic bacteria including Peptococcus, Peptostreptococcus, Eubacterium, Propionibacterium, Bacteroides and Fusobacterium was studied by agar dilution method comparing with metronidazole. In addition to this work, bactericidal effect of tinidazole and metronidazole against P. prevotii, B. fragilis ss. fragilis and F. varium was examined by quantitative culture method after incubation in GAM broth containing of 4 MIC, 2 MIC, 1 MIC and 1/2 MIC of both drugs against each of three strains for 1, 3, 6, 12 and 24 hours. All the strains of Peptococcus and Peptostreptococcus including P. anaerobius, P. saccharolyticus, P. prevotii and Ps. anaerobius and others were susceptible to a concentration of 6.25 mcg/ml of this drug. A concentration of 3.13 mcg/ml inhibited all strains of Bacteroides including B. fragilis ss. fragilis (12 strains), ss. vulgatus (5 strains), ss. thetaiotaomicron (4 strains) and ss. distasonis (2 strains). To this concentration all strains of Fusobacterium including F. varium (20 strains), F. mortiferum (2 strains) and other Fusobacterium sp. (5 strains) were susceptible. On the contrary, Propionibacterium acnes (6 strains) was resistant to 100 mcg/ml or more of tinidazole and metronidazole. The antibacterial activity of tinidazole was stronger against Bacteroides than that of metronidazole, while almost equal against Peptococcus, Peptostreptococcus, Eubacterium and Fusobacterium. Tinidazole was bactericidal against F. varium in a concentration of 2 MIC till 24 hours of incubation but did not show such an activity on B. fragilis ss. fragilis in same concentration even after 12 hours of incubation. On the other hand, metronidazole was bactericidal against B. fragilis ss. fragilis while was not against F. varium. Against P. prevotii bactericidal activity of both drugs was similar. Tinidazole as well as metronidazole is an excellent chemotherapeutic agent against anaerobic bacteria excluding Propionibacterium acnes and Bifidobacterium adolescentis.

Actinomycetaceae↗