Solc C K, Aldrich R W
Department of Neurobiology, Stanford University School of Medicine, California 94305.
J Neurosci. 1988 Jul;8(7):2556-70. doi: 10.1523/JNEUROSCI.08-07-02556.1988.
The availability of genetic, molecular, and biophysical techniques makes Drosophila an ideal system for the study of ion channel function. We have used the patch-clamp technique to characterize voltage-gated K+ channels in cultured larval Drosophila CNS neurons. Whole-cell currents from different cells vary in current kinetics and magnitude. Most of the cells contain a transient A-type 4-AP-sensitive current. In addition, many cells also have a more slowly inactivating TEA-sensitive component and/or a sustained component. No clear correlation between cell morphology and whole-cell current kinetics was observed. Single-channel analysis in cell-free patches revealed that 3 types of channels, named A2, KD, and K1 can account for the whole-cell currents. None of these channels requires elevated intracellular calcium concentration for activation. The A2 channels have a conductance of 6-8 pS and underlie the whole-cell A current. They turn on rapidly, inactivate in response to depolarizing voltage steps, and are completely inactivated by prepulses to -50 mV. The KD (delayed) channels have a conductance of 10-16 pS and can account, in part, for the more slowly inactivating component of whole-cell current. They have longer open times and activate and inactivate more slowly than the A2 channels. The K1 channels have a slope conductance, measured between 0 and +40 mV, of 20-40 pS. These channels do not inactivate during 500 msec voltage steps and thus can contribute to the sustained component of current. They exhibit complex gating behavior with increased probability of being open at higher voltages. Although the K1 channels are sufficient to account for the noninactivating component of whole-cell current, we have observed several other channel types that have a similar voltage dependence and average kinetics.
遗传、分子和生物物理技术的可用性使果蝇成为研究离子通道功能的理想系统。我们使用膜片钳技术来表征培养的果蝇幼虫中枢神经系统神经元中的电压门控钾通道。来自不同细胞的全细胞电流在电流动力学和幅度上有所不同。大多数细胞含有瞬时A 型4-氨基吡啶敏感电流。此外，许多细胞还具有失活较慢的四乙铵敏感成分和/或持续成分。未观察到细胞形态与全细胞电流动力学之间存在明显相关性。无细胞片膜的单通道分析表明，3种类型的通道，即A2、KD和K1，可以解释全细胞电流。这些通道均不需要升高的细胞内钙浓度来激活。A2通道的电导为6-8 pS，是全细胞A电流的基础。它们开启迅速，响应去极化电压阶跃而失活，并被预脉冲至-50 mV完全失活。KD（延迟）通道的电导为10-16 pS，可部分解释全细胞电流中失活较慢的成分。它们的开放时间更长，与A2通道相比，激活和失活更慢。K1通道在0至+40 mV之间测量的斜率电导为20-40 pS。这些通道在500毫秒电压阶跃期间不会失活，因此可对电流的持续成分有贡献。它们表现出复杂的门控行为，在较高电压下开放的概率增加。尽管K1通道足以解释全细胞电流的非失活成分，但我们还观察到其他几种具有相似电压依赖性和平均动力学的通道类型。
