Kulik Akos, Vida Imre, Fukazawa Yugo, Guetg Nicole, Kasugai Yu, Marker Cheryl L, Rigato Franck, Bettler Bernhard, Wickman Kevin, Frotscher Michael, Shigemoto Ryuichi
Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany.
J Neurosci. 2006 Apr 19;26(16):4289-97. doi: 10.1523/JNEUROSCI.4178-05.2006.
G-protein-coupled inwardly rectifying K+ channels (Kir3 channels) coupled to metabotropic GABAB receptors are essential for the control of neuronal excitation. To determine the distribution of Kir3 channels and their spatial relationship to GABAB receptors on hippocampal pyramidal cells, we used a high-resolution immunocytochemical approach. Immunoreactivity for the Kir3.2 subunit was most abundant postsynaptically and localized to the extrasynaptic plasma membrane of dendritic shafts and spines of principal cells. Quantitative analysis of immunogold particles for Kir3.2 revealed an enrichment of the protein around putative glutamatergic synapses on dendritic spines, similar to that of GABA(B1). Consistent with this observation, a high degree of coclustering of Kir3.2 and GABA(B1) was revealed around excitatory synapses by the highly sensitive SDS-digested freeze-fracture replica immunolabeling. In contrast, in dendritic shafts receptors and channels were found to be mainly segregated. These results suggest that Kir3.2-containing K+ channels on dendritic spines preferentially mediate the effect of GABA, whereas channels on dendritic shafts are likely to be activated by other neurotransmitters as well. Thus, Kir3 channels, localized to different subcellular compartments of hippocampal principal cells, appear to be differentially involved in synaptic integration in pyramidal cell dendrites.
与代谢型GABAB受体偶联的G蛋白偶联内向整流钾通道（Kir3通道）对于控制神经元兴奋至关重要。为了确定Kir3通道在海马锥体细胞上的分布及其与GABAB受体的空间关系，我们采用了高分辨率免疫细胞化学方法。Kir3.2亚基的免疫反应性在突触后最为丰富，定位于主细胞树突干和棘突的突触外质膜。对Kir3.2免疫金颗粒的定量分析显示，树突棘上假定的谷氨酸能突触周围该蛋白富集，类似于GABA(B1)。与此观察结果一致，通过高度敏感的SDS消化冷冻断裂复制品免疫标记，在兴奋性突触周围发现Kir3.2和GABA(B1)高度共聚集。相比之下，在树突干中，受体和通道主要是分离的。这些结果表明，树突棘上含Kir3.2的钾通道优先介导GABA的作用，而树突干上的通道可能也会被其他神经递质激活。因此，定位于海马主细胞不同亚细胞区室的Kir3通道似乎在锥体细胞树突的突触整合中发挥不同作用。
