Zhang Xiulan, Zhang Mei, Laties Alan M, Mitchell Claire H
Department of Ophthalmology, University of Pennsylvania, Philadephia, 19104, USA.
Invest Ophthalmol Vis Sci. 2005 Jun;46(6):2183-91. doi: 10.1167/iovs.05-0052.
Retinal ganglion cells are known to express ionotropic P2X(7) receptors for ATP. Stimulation of these receptors in other cells can elevate Ca(2+) and sometimes lead to cell death. This study asked whether P2X(7) receptor stimulation alters the Ca(2+) levels and viability of retinal ganglion cells.
P2X(7) agonists were applied to retinal ganglion cells from neonatal rats loaded with fura-2 to examine their effect on intracellular Ca(2+) levels. The effect of P2X(7) receptor stimulation on cell viability was examined in rat retinal ganglion cells back-labeled with aminostilbamidine.
The P2X(7) agonist benzoylbenzoyl adenosine triphosphate (BzATP) led to a large, sustained increase in Ca(2+). BzATP was >100-fold more effective than ATP at raising intracellular Ca(2+), when both agonists were applied at 10 microM. The response to BzATP was enhanced threefold by removal of extracellular Mg(2+), was dependent on extracellular Ca(2+), and was prevented by brilliant blue G (BBG). BzATP led to a concentration-dependent reduction in the number of cells with a median lethal dose (LD(50)) of 35 muM. Cell death was prevented by the P2X(7) antagonists BBG and oxidized ATP, but not by 30 microM suramin, consistent with the actions of the P2X(7) receptor. BzATP activated caspases in ganglion cells, but did not lead to membrane blebbing or increased permeability to Yo-Pro-1. The L-type Ca(2+) channel blocker nifedipine attenuated cell death, suggesting excessive Ca(2+) influx contributes to the lethal effects of BzATP.
Short-term stimulation of the P2X(7) receptor can raise Ca(2+) in rat retinal ganglion cells, whereas sustained stimulation of the receptor can kill them.
已知视网膜神经节细胞表达ATP的离子型P2X(7)受体。在其他细胞中刺激这些受体会升高Ca(2+)，有时会导致细胞死亡。本研究旨在探讨P2X(7)受体刺激是否会改变视网膜神经节细胞的Ca(2+)水平和活力。
将P2X(7)激动剂应用于负载fura-2的新生大鼠视网膜神经节细胞，以检测其对细胞内Ca(2+)水平的影响。用氨基二苯乙烯脒反向标记的大鼠视网膜神经节细胞中检测P2X(7)受体刺激对细胞活力的影响。
P2X(7)激动剂苯甲酰苯甲酰三磷酸腺苷（BzATP）导致Ca(2+)大幅持续升高。当两种激动剂均以10 microM应用时，BzATP在升高细胞内Ca(2+)方面比ATP有效>100倍。去除细胞外Mg(2+)可使对BzATP的反应增强三倍，该反应依赖于细胞外Ca(2+)，并被亮蓝G（BBG）阻断。BzATP导致细胞数量呈浓度依赖性减少，半数致死剂量（LD(50)）为35 microM。P2X(7)拮抗剂BBG和氧化ATP可防止细胞死亡，但30 microM的苏拉明则不能，这与P2X(7)受体的作用一致。BzATP激活神经节细胞中的半胱天冬酶，但不会导致细胞膜起泡或对Yo-Pro-1的通透性增加。L型Ca(2+)通道阻滞剂硝苯地平可减轻细胞死亡，提示过量的Ca(2+)内流有助于BzATP的致死作用。
短期刺激P2X(7)受体可使大鼠视网膜神经节细胞中的Ca(2+)升高，而持续刺激该受体则可杀死这些细胞。
