Publications by authors named "URAKAWA N"

The effects of vanadate on tension and on the Na-K pump in isolated guinea-pig aorta were investigated. Vanadates (NH4VO3 or Na3VO4 . nH2O) (10(-3) M) produced a sustained contraction (about 0.

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Isosmotic substitution of KCl for NaCl in the physiological solution produces a transient contraction while KCl added hyperosmotically to the physiological solution produces a sustained contraction in guinea-pig taenia coli. Wet weight of the tissue increased in the high K, Na deficient solution. Hyperosmotically added sucrose completely prevented the increase in wet weight although the inhibition of sustained contraction was only partly (approximately 25%) recovered.

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In Ca-free solution norepinephrine (NE) produced only a phasic contraction in the media-intima layer of rabbit aorta. The second application of NE was almost ineffective. Incubation of the muscle with Ca for a short period (Ca loading) restored the ability to produce a phasic contraction in Ca-free solution.

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Effects of palytoxin (PTX) on isolated papillary muscles of guinea pigs were studied in an attempt to elucidate the mechanical and electrical activities. Inotropic effects of PTX above 3 x 10(-9) g/ml; an early positive inotropic effect, slowly developing contracture accompanied by decline in phasic tension, appearance of aftercontractions and arrhythmias at high doses. The positive inotropic effect of PTX was enhanced in high Ca2+ medium but was not modified by propranolol.

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The properties of contractions induced by ouabain and by K depletion were studied in comparison with those induced by other stimulants in guinea pig taenia coli. Ouabain 7.5 X 10(-6) M and K depletion produced biphasic contractions with similar time courses.

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Ouabain and K-free solution affected the tension development of isolated vessels as follows. In rabbit aorta, ouabain induced a transient contraction followed by a delayed sustained contraction whereas K-free solution was almost ineffective; both ouabain and K-free solution produced a sustained contraction in guinea pig aorta; rat aorta rarely responded to ouabain but developed a contraction in K-free solution. Phentolamine inhibited the transient contraction produced by ouabain in rabbit aorta.

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The differential effects of papaverine (Pap) and rotenone (Rot) were studied on the highly respiration-dependent contracture of guinea pig taenia coli in 40 mM potassium (40-K) medium, on isolated DT diaphorase activity and on mitochondrial respiration. The inhibition of guinea pig taenia coli to the 40-K induced tension by Rot (5 x 10(-7)M) was fully reversed by the addition of a water soluble vitamin K3 (VK3) derivative or menadione sodium bisulfite (MSB). A low concentration (10(-7)--10(-6)M) of Pap which had no effect on the 40-K induced tension inhibited the VK3 restored tension from the Rot suppression, corresponding to a Pap inhibition of the isolated DT diaphorase.

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Papaverine (Pap) inhibited a tonic tension development in guinea pig taenia coli induced by an elevation of the potassium concentration of the medium to 40 mM (40-K). The ID50 of Pap was 4.5 x 10(-6) M.

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Experiments were designed to assess the mode of action of palytoxin (PTX), isolated from Palythoa tuberculosa, on mechanically denervated rabbit aortic strips. PTX induced a sustained contraction in the muscle dose dependently. The contraction was irreversible.

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Effects of ouabain, Na+ depletion and K+ depletion on the tension development of rabbit aorta were studied. Contraction in the strips was induced by ouabain and Na+-free solution substituted with Li+, tris or sucrose. The contractions were rarely seen under alpha-adrenergic blockade, in reserpinized aorta and mechanically denervated aorta.

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Palytoxin (PTX), the most potent marine toxin isolated from the Zoanthid, Palythoa tuberculosa, was studied to determine the effect on isolated smooth muscles. In guinea pig taenia coli PTX at above 3 X 10(-10) g/ml caused a contraction which slowly subsided under isotonic recording. Under isometric recording PTX at above 1 X 10(-10) g/ml caused a contraction which depended on the spontaneous activity.

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