Molecular Neurophysiology and Biophysics Unit, Laboratory of Cellular and Synaptic Neurophysiology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892-3715, USA.
Hippocampus. 2012 May;22(5):969-80. doi: 10.1002/hipo.20899. Epub 2011 Apr 6.
The heterogeneous expression of voltage-gated channels in dendrites suggests that neurons perform local microdomain computations at different regions. It has been shown that A-type K(+) channels have a nonuniform distribution along the primary apical dendrite in CA1 pyramidal neurons, increasing with distance from the soma. Kv4.2 channels, which are responsible for the somatodendritic A-type K(+) current in CA1 pyramidal neurons, shape local synaptic input, and regulate the back-propagation of APs into dendrites. Experiments were performed to test the hypothesis that Kv4.2 channels are differentially trafficked at different regions along the apical dendrite during basal activity and upon stimulation in CA1 neurons. Proximal (50-150 μm from the soma, primary and oblique) and distal (>200 μm) apical dendrites were selected. The fluorescence recovery after photobleaching (FRAP) technique was used to measure basal cycling rates of EGFP-tagged Kv4.2 (Kv4.2g). We found that the cycling rate of Kv4.2 channels was one order of magnitude slower at both primary and oblique dendrites between 50 and 150 μm from the soma. Kv4.2 channel cycling increased significantly at 200 to 250 μm from the soma. Expression of a Kv4.2 mutant lacking a phosphorylation site for protein kinase-A (Kv4.2gS552A) abolished this distance-dependent change in channel cycling; demonstrating that phosphorylation by PKA underlies the increased mobility in distal dendrites. Neuronal stimulation by α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) treatment increased cycling of Kv4.2 channels significantly at distal sites only. This activity-dependent increase in Kv4.2 cycling at distal dendrites was blocked by expression of Kv4.2gS552A. These results indicate that distance-dependent Kv4.2 mobility is regulated by activity-dependent phosphorylation of Kv4.2 by PKA.
电压门控通道在树突中的异质表达表明，神经元在不同区域执行局部微域计算。已经表明，在 CA1 锥体神经元的初级树突中，A 型 K(+)通道沿树突呈非均匀分布，距离胞体越远，分布越多。Kv4.2 通道负责 CA1 锥体神经元的胞体-树突 A 型 K(+)电流，它可以调节局部突触输入，并调节动作电位逆行传入树突。实验目的是检验假设，即在 CA1 神经元的基础活动和刺激期间，Kv4.2 通道在树突的不同区域以不同的方式运输。选择了近侧（距胞体 50-150μm，初级和斜侧）和远侧（>200μm）树突。使用荧光恢复后漂白（FRAP）技术测量 EGFP 标记的 Kv4.2（Kv4.2g）的基础循环率。结果发现，在距胞体 50-150μm 的初级和斜侧树突中，Kv4.2 通道的循环率慢一个数量级。在距胞体 200-250μm 处，Kv4.2 通道的循环率显著增加。表达缺乏蛋白激酶 A（PKA）磷酸化位点的 Kv4.2 突变体（Kv4.2gS552A）消除了这种通道循环的距离依赖性变化；表明 PKA 的磷酸化是在远端树突中增加迁移率的基础。只有在远端部位，用 α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）处理神经元刺激会显著增加 Kv4.2 通道的循环。在远端树突中，这种依赖于活性的 Kv4.2 循环增加被 Kv4.2gS552A 的表达所阻断。这些结果表明，Kv4.2 迁移的距离依赖性由 PKA 依赖性磷酸化调节。
