歩調取り細胞のリズムの支配について

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タイトル別名
  • DOMINANCE OF RHYTHM IN THE PACEMAKER CELL
  • ホチョウシュリ サイボウ ノ リズム ノ シハイ ニ ツイテ

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It is well known that the dominant pacemaker in the heart exists in a faster beating site rather than a slowly beating one. In this experiment we found that the dominant pacemaker site in the frog's sinus venosus was not always subject to the above law, when the pacemaker shift was arising from vagus stimulation. In all experiments the heart was excised together with the vagosympathetic nerve. The ventricle and large part of the auricles were cut away. A vagosympathetic nerve-sinus preparation was perfused with Ringer's solution saturated with 95% O2 + 5% CO2.<BR>Intracellularly were recorded changes of pacemaker potential just during and after the stimulation of the vagus nerve. When the stimulation was applied with a certain strength and frequency, the normal pacemaker potential was separated from the prepotential and it showed a shift of dominant pacemaker site where an ectopic pacemaker was generated in a same sinus. In this case the rhythm of the sinus was under control of a new shifting site, but the intrinsic pacemaker was still remained underground. The new dominant pacemaker was generally a more slowly beating rate than the intrinsic, once a while, faster than the intrinsic. If the stimulation was removed, the intrinsic pacemaker was gradually recovered and dominated the sinus again.<BR>In conclussion the presented results suggest that under abnormal circumstance ectopic pacemaker action can develop, compete with the normal pacemaker, and the ectopic pacemaker begins to drive the sinus temporarily, but finally it is replaced by the intrinsic pacemaker after destruction of abnormal circumstance. The abilities which dominate the rythm of pacemaker cell are dependent not only on beating rate but also on other many factors, that is, size, number, combination of true cell groups and conjunction with the nerve terminals.

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