| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 1998: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Specificity of mice myocardium and its functional changes during development were examined from various points of veiw (electrophysiology, contractile mechanisms, drug sensitivity, etc.). Main results obtained are as follows.
1)Action potentials with relatively long duration at neonatal stages were changed into those with extremetly short duration without plateau phase in the adult. This characteristic action potential configuration was considered to be due to small calcium current and large transient outward current, which was essentially the same as that observed in rat myocardium. During development, calcium current seemed to decrease with age.
2)Contraction of adult myocardium was suggested to be highly dependent on SR function whereas the dependency was low in neonatal myocardium. This change was qualitatively similar to that observed in rat myocardium, but the degree of developmental change was small compared to rat.
3)Developmental conversion of inotropism from positive to negative was observed in the responses to endothelin I and angiotensin II, which was similar to that observed with alpha-adrenergic stimulation. Receptor subtypes did not change during development (ETA and AT1, respectively)
4)Acetylcholine produced positive inotropic response in mouse atria, which was totally different from other animal species. On the basis of various experimental results, it was suggested that acetylcholine may release prostaglandin(s) from endocardial endothelial cells, which in turn producced positive inotropism.
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