Wagoner P K, Oxford G S
Department of Pharmacology, GLAXO Research Laboratories, Research Triangle Park, North Carolina 27709.
Biophys J. 1990 Dec;58(6):1481-9. doi: 10.1016/S0006-3495(90)82493-0.
The blocking action of aminopyridines on an inactivating K current (lKi) in GH3 pituitary cells was studied before and after altering the macroscopic decay of the current with N-bromoacetamide (NBA). The first depolarizing pulse delivered either seconds or minutes after beginning 4-aminopyridine (4AP) application, elicited a current with both a more rapid decay and a reduced peak amplitude. The rapid decay (or time-dependent block) was especially prominent in NBA-treated cells. With continued drug application, subsequent test pulses revealed a stable block of peak current, greater in NBA-treated than control cells. Recovery from block was enhanced by hyperpolarizing holding potentials and by the first depolarizing pulse delivered after prolonged recovery intervals. Unlike aminopyridine block of other K currents, there was no convincing evidence for voltage shifts in activation or inactivation, or for voltage and frequency-dependent unblock. Increasing the open probability of the channels did, however, facilitate the block. Although the behavior of currents in 4AP was suggestive of "open channel block," the block was not produced by 4-aminopyridine methiodide, a positively charged aminopyridine. Moreover, because partial block and recovery occurred without opening the channels we suggest that aminopyridines bind to, or near, this K channel, that this binding is enhanced by opening the channel, and that a conformational change is induced which mimics inactivation. Because recovery from block is enhanced by negative potentials, we suggest that aminopyridine molecules may become "trapped" by inactivation awaiting the slow process of reactivation to escape their binding sites.
在利用N-溴代乙酰胺（NBA）改变生长激素释放激素（GH3）垂体细胞中一种失活钾电流（lKi）的宏观衰减之前和之后，研究了氨基吡啶对该电流的阻断作用。在开始应用4-氨基吡啶（4AP）后的几秒或几分钟施加的第一个去极化脉冲，引发了一种衰减更快且峰值幅度降低的电流。快速衰减（或时间依赖性阻断）在经NBA处理的细胞中尤为显著。持续应用药物后，随后的测试脉冲显示峰值电流出现稳定的阻断，经NBA处理的细胞中的阻断作用比对照细胞更强。通过超极化钳制电位以及在长时间恢复间隔后施加的第一个去极化脉冲，可增强从阻断状态的恢复。与氨基吡啶对其他钾电流的阻断不同，没有令人信服的证据表明激活或失活存在电压偏移，也没有证据表明存在电压和频率依赖性的解阻断。然而，增加通道的开放概率确实会促进阻断作用。尽管4AP中电流的行为提示“开放通道阻断”，但这种阻断并非由带正电荷的氨基吡啶——4-氨基吡啶甲碘化物产生。此外，由于在通道未开放的情况下也会出现部分阻断和恢复，我们认为氨基吡啶与该钾通道或其附近结合，通道开放会增强这种结合，并且会诱导一种构象变化，这种变化模拟了失活状态。由于负电位可增强从阻断状态的恢复，我们认为氨基吡啶分子可能因失活而“被困住”，等待缓慢的再激活过程以逃离其结合位点。
