Gordon T R, Kocsis J D, Waxman S G
Department of Neurology, Yale Medical School, New Haven, CT.
Brain Res. 1989 Nov 20;502(2):252-7. doi: 10.1016/0006-8993(89)90620-3.
Optic nerves were removed from 4-8-week-old rats and studied in a modified sucrose gap chamber in order to examine the pharmacological sensitivities of two afterhyperpolarizations (AHPs), an early and a late one. The peak latency of the early AHP, which occurred immediately after the action potential, was 6-12 ms, and its duration was 44-75 ms. The early AHP was present at resting potential in about 75% of recorded nerves. In the nerves in which an early AHP was not present at resting potential, an AHP was present during delivery of constant current depolarization through the sucrose gap. The early AHP was increased in amplitude by depolarization of the nerve, decreased in amplitude or reversed in polarity by hyperpolarization, was not affected by tetraethylammonium (TEA) or Co2+, and was obliterated by 4-aminopyridine (4-AP) concomitant with action potential broadening. The late AHP followed a broadened action potential in the presence of the potassium channel blocker 4-AP. Its peak latency ranged from 112 to 254 ms and its duration from 336 to 710 ms. It was increased in amplitude with repetitive stimulation, was reversibly obliterated by TEA, but was not significantly altered by Co2+, Cd2+, Ca2+ removal, charybdotoxin or apamin. The results demonstrate the presence of two AHPs mediated by pharmacologically distinct potassium conductances in rat optic nerve, neither of which is calcium-dependent.
从4至8周龄大鼠中取出视神经，在改良的蔗糖间隙室中进行研究，以检测两种超极化后电位（AHPs），即早期和晚期超极化后电位的药理学敏感性。早期超极化后电位在动作电位之后立即出现，其峰值潜伏期为6至12毫秒，持续时间为44至75毫秒。在约75%的记录神经中，早期超极化后电位存在于静息电位时。在静息电位时不存在早期超极化后电位的神经中，在通过蔗糖间隙施加恒流去极化期间存在超极化后电位。神经去极化可使早期超极化后电位的幅度增加，超极化则使其幅度减小或极性反转，其不受四乙铵（TEA）或Co2+的影响，并且在4-氨基吡啶（4-AP）使动作电位增宽的同时被消除。晚期超极化后电位在存在钾通道阻滞剂4-AP的情况下跟随增宽的动作电位出现。其峰值潜伏期为112至254毫秒，持续时间为336至710毫秒。重复刺激可使其幅度增加，TEA可使其可逆性消除，但Co2+、Cd2+、去除Ca2+、芋螺毒素或蜂毒明肽对其无明显影响。结果表明，大鼠视神经中存在两种由药理学上不同的钾电导介导的超极化后电位，两者均不依赖于钙。
