DIFFERENTIAL CONDUCTION BLOCK IN BRANCHES OF A BIFURCATING AXON
DIFFERENTIAL CONDUCTION BLOCK IN BRANCHES OF A BIFURCATING AXON
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DOI：
10.1113/jphysiol.1979.sp012969
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发表时间：
1979-01-01
影响因子：
5.5
通讯作者：
SPIRA, ME
中科院分区：
文献类型：
--
作者：
GROSSMAN, Y;PARNAS, I;SPIRA, ME
用同时记录的方法研究了龙虾（Panulirus penicillatus）分支轴突前后的高频动作电位的传播。尽管所研究的分支轴突具有接近1的几何比（完美阻抗匹配），但在刺激频率高于30hz时，分支点的传导失败。高频刺激后的传导阻滞发生在分支点本身。母轴突和子分支继续传导动作电位。高频刺激后的传导阻滞首先出现在较粗的子支，随后才出现在较细的子支。在高频刺激下，亲本轴突动作电位幅值下降10-15%，动作电位上升速率相应下降，传导速度下降25-30%，阈值明显升高，不应期延长。膜去极化1- 3mv。使用膜片钳技术测量的膜电流显示，在分支点之前，与动作电位相关的相内电流大幅减少。高频刺激后小的膜去极化并不是导致传导阻滞的唯一原因。施加长时间的膜去极化（8 mV 120 s）不足以产生传导阻滞。来自主神经束（包含母轴突）和大子分支的体内慢性细胞外记录显示，沿轴突的动作电位序列的持续时间和频率超过了在孤立神经实验中使用的时间和频率，并且通过电刺激主分支可以在整个动物中引起大子分支的传导失败，就像在孤立准备中一样。讨论了分支轴突高频刺激后传导阻滞的可能机制。
Propagation of action potentials at high frequency was studied in a branching axon of the lobster [Panulirus penicillatus] by means of simultaneous intracellular recording before and after the branch point. Although the branching axon studied has a geometrical ratio close to 1 (perfect impedance matching) conduction across the branch point failed at stimulation frequencies above 30 Hz. The block of conduction after high frequency stimulation occurred at the branch point per se. The parent axon and daughter branches continued to conduct action potentials. Conduction block after high frequency stimulation appeard first in the thicker daugher branch and only later in the thin branch. With high frequency stimulation there was a 10-15% reduction in amplitude of the action potential in the parent axon, a corresponding decrease in the rate of rise of the action potential, a 25-30% decrease in conduction velocity, marked increase in threshold and prolongation of the refractory period. The membrane was depolarized by 1-3 mV. Measurements of the membrane current using the patch clamp technique showed a large decrease in the phase inward current associated with the action potential, before the branching point. The small membrane depolarization seen after high frequency stimulation was not the sole cause of the conduction block. Imposed prolonged membrane depolarization (8 mV for 120 s) was insufficient to produce conduction block. In vivo chronic extracellular recordings from the main nerve bundle (which contains the parent axon) and the large daughter branch revealed that the duration and frequency of trains of action potentials along the axons exceeded those used in the isolated nerve experiments and conduction failure in the large daughter branch could be induced in the whole animal by electrical stimulation of the main branch as in the isolated preparation. Possible mechanisms underlying block of conduction after high frequency stimulation in a branching axon are discussed.