Gordon T R, Kocsis J D, Waxman S G
Department of Neurology, Yale University School of Medicine, New Haven, CT 06510.
Brain Res. 1988 Apr 26;447(1):1-9. doi: 10.1016/0006-8993(88)90959-6.
Single axon and whole nerve recording techniques were used to study the effects of 4-aminopyridine (4-AP) and tetraethylammonium (TEA) on action potential waveform and firing characteristics of rat optic nerve. 4-AP led to action potential broadening and a pronounced afterhyperpolarization (AHP) several hundreds of milliseconds in duration. In addition, some fibers showed repetitive firing and a prolonged depolarization immediately following the spike. Whole nerve sucrose gap recordings obtained in the presence of 4-AP showed action potential broadening followed by a postspike positivity indicative of intracellular hyperpolarization. The time course of the postspike positivity was similar to that of the AHP seen in single fiber recordings. TEA alone had little effect on action potential waveform, but reversibly blocked the 4-AP-induced postspike positivity. These findings indicate the presence of two pharmacologically distinct potassium channels on myelinated axons of the rat optic nerve, one sensitive to 4-AP and the other to TEA. These channels appear to have different functional roles, the 4-AP-sensitive channel participating in action potential repolarization, and the TEA-sensitive channel modulating repetitive firing patterns.
采用单轴突和全神经记录技术，研究4-氨基吡啶（4-AP）和四乙铵（TEA）对大鼠视神经动作电位波形及放电特性的影响。4-AP导致动作电位增宽，并出现持续数百毫秒的明显超极化后电位（AHP）。此外，一些纤维在锋电位后立即出现重复放电和延长的去极化。在4-AP存在下进行的全神经蔗糖间隙记录显示动作电位增宽，随后出现锋电位后阳性，提示细胞内超极化。锋电位后阳性的时间进程与单纤维记录中观察到的AHP相似。单独使用TEA对动作电位波形影响不大，但可可逆地阻断4-AP诱导的锋电位后阳性。这些发现表明，在大鼠视神经的有髓轴突上存在两种药理学特性不同的钾通道，一种对4-AP敏感，另一种对TEA敏感。这些通道似乎具有不同的功能作用，4-AP敏感通道参与动作电位复极化，而TEA敏感通道调节重复放电模式。
