Abiru Y, Katoh-Semba R, Nishio C, Hatanaka H
Division of Protein Biosynthesis, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Brain Res. 1998 Oct 26;809(1):115-26. doi: 10.1016/s0006-8993(98)00849-x.
Elevation of extracellular potassium concentration ([K+]o) in the central nervous system (CNS), which is observed such after physiological stimuli and during ischemia, is known to be regulated by astrocytes. We suspected that in response to increased [K+]o, astrocytes might secrete some neurotrophic factor(s) to promote the survival of active and/or ischemically damaged neurons. In the present study, we examined neurotrophic activity contained in HK-ACM, i.e., astrocyte-conditioned medium (ACM) obtained after culturing astrocytes in 40 mM potassium-containing medium (HK medium). Addition of HK-ACM to basal forebrain cultures from postnatal 2-week-old (P2w) rats increased both the choline acetyltransferase (ChAT) activity (4.40-fold) and the number of ChAT-positive neurons (2.01-fold) as compared with non-conditioned HK medium. On the other hand, the neurotrophic effects of LK-ACM, i.e., ACM collected after culturing astrocytes in 4 mM potassium-containing medium (LK medium), were much weaker (2.85- and 1.41-fold for ChAT activity and number of ChAT-positive neurons, respectively) than those of HK-ACM. The neurotrophic effects of ACMs increased in a manner dependent on potassium concentration and on astrocyte culture time. Addition of an antibody against nerve growth factor (NGF) neutralized the neurotrophic effects of HK- and LK-ACMs. Direct quantification of NGF protein in ACMs by the two-site ELISA method demonstrated that a high concentration of potassium enhanced NGF secretion from cultured astrocytes. These results suggested that astrocytes secrete NGF in response to [K+]o elevation in the CNS.
中枢神经系统（CNS）细胞外钾离子浓度（[K+]o）升高，在生理刺激后以及缺血期间均可观察到，已知其受星形胶质细胞调节。我们推测，响应[K+]o升高，星形胶质细胞可能会分泌一些神经营养因子，以促进活跃和/或缺血损伤神经元的存活。在本研究中，我们检测了HK-ACM中的神经营养活性，即星形胶质细胞条件培养基（ACM），它是在含40 mM钾的培养基（HK培养基）中培养星形胶质细胞后获得的。与未处理的HK培养基相比，向出生后2周龄（P2w）大鼠的基底前脑培养物中添加HK-ACM可使胆碱乙酰转移酶（ChAT）活性提高4.40倍，ChAT阳性神经元数量增加2.01倍。另一方面，LK-ACM的神经营养作用，即星形胶质细胞在含4 mM钾的培养基（LK培养基）中培养后收集得到的ACM，比HK-ACM弱得多（ChAT活性和ChAT阳性神经元数量分别为2.85倍和1.41倍）。ACMs的神经营养作用以依赖钾浓度和星形胶质细胞培养时间的方式增加。添加抗神经生长因子（NGF）抗体可中和HK-ACM和LK-ACM的神经营养作用。通过双位点ELISA方法直接定量ACM中的NGF蛋白表明，高浓度钾可增强培养的星形胶质细胞分泌NGF。这些结果表明，星形胶质细胞在CNS中响应[K+]o升高而分泌NGF。
