Interdepartmental Neuroscience Program, Northwestern University, Evanston, Illinois, USA.
J Neurophysiol. 2013 May;109(10):2528-41. doi: 10.1152/jn.00127.2012. Epub 2013 Feb 27.
Purkinje cells have specialized intrinsic ionic conductances that generate high-frequency action potentials. Disruptions of their Ca or Ca-activated K (KCa) currents correlate with altered firing patterns in vitro and impaired motor behavior in vivo. To examine the properties of somatic KCa currents, we recorded voltage-clamped KCa currents in Purkinje cell bodies isolated from postnatal day 17-21 mouse cerebellum. Currents were evoked by endogenous Ca influx with approximately physiological Ca buffering. Purkinje somata expressed voltage-activated, Cd-sensitive KCa currents with iberiotoxin (IBTX)-sensitive (>100 nS) and IBTX-insensitive (>75 nS) components. IBTX-sensitive currents activated and partially inactivated within milliseconds. Rapid, incomplete macroscopic inactivation was also evident during 50- or 100-Hz trains of 1-ms depolarizations. In contrast, IBTX-insensitive currents activated more slowly and did not inactivate. These currents were insensitive to the small- and intermediate-conductance KCa channel blockers apamin, scyllatoxin, UCL1684, bicuculline methiodide, and TRAM-34, but were largely blocked by 1 mM tetraethylammonium. The underlying channels had single-channel conductances of ∼150 pS, suggesting that the currents are carried by IBTX-resistant (β4-containing) large-conductance KCa (BK) channels. IBTX-insensitive currents were nevertheless increased by small-conductance KCa channel agonists EBIO, chlorzoxazone, and CyPPA. During trains of brief depolarizations, IBTX-insensitive currents flowed during interstep intervals, and the accumulation of interstep outward current was enhanced by EBIO. In current clamp, EBIO slowed spiking, especially during depolarizing current injections. The two components of BK current in Purkinje somata likely contribute differently to spike repolarization and firing rate. Moreover, augmentation of BK current may partially underlie the action of EBIO and chlorzoxazone to alleviate disrupted Purkinje cell firing associated with genetic ataxias.
浦肯野细胞具有特殊的内在离子电导，可产生高频动作电位。它们的钙或钙激活钾（KCa）电流的中断与体外放电模式的改变和体内运动行为的损害有关。为了研究体细胞 KCa 电流的特性，我们记录了从出生后第 17-21 天的小鼠小脑分离的浦肯野细胞体的电压钳制 KCa 电流。电流是由内源性钙内流引起的，并用约生理的钙缓冲液进行缓冲。浦肯野体细胞表达电压激活、Cd 敏感的 KCa 电流，具有 iberiotoxin（IBTX）敏感（>100 nS）和 IBTX 不敏感（>75 nS）成分。IBTX 敏感的电流在几毫秒内激活并部分失活。在 50 或 100-Hz 的 1-ms 去极化脉冲串中，也可以明显观察到快速、不完全的宏观失活。相比之下，IBTX 不敏感的电流激活得更慢，不会失活。这些电流对小电导和中间电导 KCa 通道阻断剂 apamin、scyllatoxin、UCL1684、bicuculline methiodide 和 TRAM-34 不敏感，但被 1 mM 四乙铵大部分阻断。潜在的通道具有约 150 pS 的单通道电导，表明电流由 IBTX 抗性（含β4）大电导 KCa（BK）通道携带。然而，小电导 KCa 通道激动剂 EBIO、氯唑沙宗和 CyPPA 仍可增加 IBTX 不敏感的电流。在短暂去极化脉冲串期间，IBTX 不敏感的电流在步间间隔期间流动，EBIO 增强了步间外向电流的积累。在电流钳制下，EBIO 减缓了尖峰，尤其是在去极化电流注入期间。浦肯野体细胞中 BK 电流的两个成分可能对尖峰复极化和放电率有不同的贡献。此外，BK 电流的增强可能部分解释了 EBIO 和氯唑沙宗缓解与遗传共济失调相关的浦肯野细胞放电紊乱的作用。
