Wu R L, Butler D M, Barish M E
Division of Neurosciences, Beckman Research Institute of the City of Hope, Duarte, California 91010, USA.
J Neurosci. 1998 Aug 15;18(16):6261-78. doi: 10.1523/JNEUROSCI.18-16-06261.1998.
Hippocampal pyramidal neurons express three major voltage-dependent potassium currents, IA, ID, and IK. During hippocampal development, IA, the rapidly activating and inactivating transient potassium current, is detected soon after pyramidal neurons can be morphologically identified. Appearance of IA in developing pyramidal neurons is dependent on contact with cocultured astroglial cells; cultured pyramidal neurons not in contact with astroglial cells have reduced membrane area and IA (Wu and Barish, 1994). We have examined intracellular signaling pathways that could contribute to the regulation of IA development by probing developing pyramidal neurons with kinase inhibitors. We observed that exposure to LY294002 or wortmannin, inhibitors of phosphatidylinositol (PI) 3-kinase, reduced somatic cross-sectional area, neurite outgrowth, whole-cell capacitance, IA amplitude and density (amplitude normalized to membrane area), and immunoreactivity for Kv4.2 and/or Kv4.3 (potassium channel subunits likely to be present in the channels carrying IA). In contrast, exposure to ML-9 or KN-62, inhibitors of myosin light chain kinase or Ca2+-calmodulin-dependent protein kinase II (CaMKII), reduced membrane area and IA amplitude but did not affect IA density or Kv4. 2/3 immunoreactivity to the same extent as inhibitors of PI 3-kinase. Unexpectedly, exposure to bisindolymaleimide I or calphostin C, inhibitors of protein kinase C (PKC), did not affect membrane area or potassium current development. Our data suggest that PI 3-kinases regulate both A-type potassium channel synthesis and plasmalemmal insertion of vesicles bearing these potassium channels. CaMKII appears to regulate fusion of channel-bearing vesicles with the plasmalemma and myosin light chain kinase to regulate centripetal transport of channel-bearing vesicles from the Golgi. We further suggest that astroglial cells exert their influence on pyramidal neuron development through activation of PI 3-kinases.
海马锥体神经元表达三种主要的电压依赖性钾电流，即IA、ID和IK。在海马发育过程中，IA是一种快速激活和失活的瞬时钾电流，在锥体神经元在形态上可被识别后不久就能检测到。发育中的锥体神经元中IA的出现依赖于与共培养的星形胶质细胞的接触；未与星形胶质细胞接触的培养锥体神经元的膜面积和IA减少（Wu和Barish，1994）。我们通过用激酶抑制剂刺激发育中的锥体神经元，研究了可能有助于调节IA发育的细胞内信号通路。我们观察到，暴露于磷脂酰肌醇（PI）3激酶抑制剂LY294002或渥曼青霉素会降低体细胞横截面积、神经突生长、全细胞电容、IA幅度和密度（幅度相对于膜面积进行归一化），以及Kv4.2和/或Kv4.3（可能存在于携带IA的通道中的钾通道亚基）的免疫反应性。相比之下，暴露于肌球蛋白轻链激酶抑制剂ML-9或Ca2+ - 钙调蛋白依赖性蛋白激酶II（CaMKII）抑制剂KN-62会降低膜面积和IA幅度，但对IA密度或Kv4.2/3免疫反应性的影响程度不如PI 3激酶抑制剂。出乎意料的是，暴露于蛋白激酶C（PKC）抑制剂双吲哚马来酰亚胺I或钙磷蛋白C对膜面积或钾电流发育没有影响。我们的数据表明，PI 3激酶调节A型钾通道的合成以及携带这些钾通道的囊泡向质膜的插入。CaMKII似乎调节携带通道的囊泡与质膜的融合，而肌球蛋白轻链激酶调节携带通道的囊泡从高尔基体向心运输。我们进一步表明，星形胶质细胞通过激活PI 3激酶对锥体神经元发育发挥其影响。
