Coco Silvia, Calegari Federico, Pravettoni Elena, Pozzi Davide, Taverna Elena, Rosa Patrizia, Matteoli Michela, Verderio Claudia
Consiglio Nazionale delle Ricerche Institute of Neuroscience, Cellular and Molecular Pharmacology, Department of Medical Pharmacology, University of Milano, Italy.
J Biol Chem. 2003 Jan 10;278(2):1354-62. doi: 10.1074/jbc.M209454200. Epub 2002 Oct 31.
ATP is released from astrocytes and is involved in the propagation of calcium waves among them. Neuronal ATP secretion is quantal and calcium-dependent, but it has been suggested that ATP release from astrocytes may not be vesicular. Here we report that, besides the described basal ATP release facilitated by exposure to calcium-free medium, astrocytes release purine under conditions of elevated calcium. The evoked release was not affected by the gap-junction blockers anandamide and flufenamic acid, thus excluding purine efflux through connexin hemichannels. Sucrose-gradient analysis revealed that a fraction of ATP is stored in secretory granules, where it is accumulated down an electrochemical proton gradient sensitive to the v-ATPase inhibitor bafilomycin A(1). ATP release was partially sensitive to tetanus neurotoxin, whereas glutamate release from the same intoxicated astrocytes was almost completely impaired. Finally, the activation of metabotropic glutamate receptors, which strongly evokes glutamate release, was only slightly effective in promoting purine secretion. These data indicate that astrocytes concentrate ATP in granules and may release it via a regulated secretion pathway. They also suggest that ATP-storing vesicles may be distinct from glutamate-containing vesicles, thus opening up the possibility that their exocytosis is regulated differently.
三磷酸腺苷（ATP）由星形胶质细胞释放，并参与其中钙波的传播。神经元的ATP分泌是量子化且依赖钙的，但有人提出星形胶质细胞释放ATP可能不是通过囊泡进行的。在此我们报告，除了在无钙培养基中暴露所促进的所述基础ATP释放外，星形胶质细胞在钙浓度升高的条件下也会释放嘌呤。诱发释放不受缝隙连接阻滞剂花生四烯酸乙醇胺和氟芬那酸的影响，因此排除了通过连接蛋白半通道的嘌呤外流。蔗糖梯度分析显示，一部分ATP储存在分泌颗粒中，在那里它沿着对V-ATP酶抑制剂巴弗洛霉素A（1）敏感的电化学质子梯度积累。ATP释放对破伤风神经毒素部分敏感，而来自相同中毒星形胶质细胞的谷氨酸释放几乎完全受损。最后，代谢型谷氨酸受体的激活，虽然强烈诱发谷氨酸释放，但在促进嘌呤分泌方面效果甚微。这些数据表明，星形胶质细胞将ATP浓缩在颗粒中，并可能通过一种受调控的分泌途径释放它。它们还表明，储存ATP的囊泡可能与含谷氨酸的囊泡不同，因此开启了它们的胞吐作用可能受到不同调控的可能性。
