心筋のBa誘発自動能に見いだされた過剰興奮期と新しい膜電流(食物栄養学科編)

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The excitability recovery characteristics and membrane voltage and current during the diastolic period in Ba-induced pacemaker activity were examined in the bullfrog atrial muscle by means of double sucrose-gap techniques. The afterhyperpolarization, facilitating the deactivation of the delayed outward current (I_x), steepened the slope of phase 4 depolarization. This and concomitant increase in membrane resistance and electrotonic potential during the depolarization produced an increase in electrical excitability. A supernormal period in excitability was elucidated at the later phase of the diastolic slow depolarization. The possible causes were, (a) an appearance of specific inward current related to electrogenic Na-Ca exchange which superimposed on the tail of I_x, (b) a presence of the transient inward current (I_<TI>), and (c ) a biphasic recovery of the slow inward current (I_<si>) at the later phase of the pecemaker depolrization. Depolarization-induced pacemakers, perhaps the true pacemaker in the S-A node as well, may well utilize the supernormal excitability in sustaining automaticity.
中村学園大学の論文
1987-03-31