Studies on the developmental changes and species difference of cardiac function : analysis of the electrophysiological characteristics and specific responses to alpha-adrenergic stimulation in mice

从电生理、收缩机制、药物敏感性等角度考察小鼠心肌的特异性及其在发育过程中的功能变化。得到的主要结果如下。1)新生儿期持续时间较长的动作电位在成年期转变为持续时间极短且无平台期的动作电位。这种特征性动作电位配置被认为是由于钙电流小，瞬态外向电流大，这与大鼠心肌基本相同。在发育过程中，钙电流似乎随着年龄的增长而降低。2)成人心肌的收缩高度依赖于SR功能，而新生儿心肌的收缩依赖程度较低。这种变化在质量上与大鼠心肌相似，但与大鼠相比，发育变化的程度较小。3)内皮素I和血管紧张素II对肌力的反应由阳性向阴性转变，这与α -肾上腺素能刺激的结果相似。受体亚型在发育过程中没有发生变化（分别为ETA和AT1）。4)乙酰胆碱在小鼠心房产生正性肌力反应，这与其他动物完全不同。根据各种实验结果，我们认为乙酰胆碱可能从心内膜内皮细胞释放前列腺素，从而产生正性肌力。

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.