Stimulation of P2X7Receptors Elevates Ca2+and Kills Retinal Ganglion Cells

Xiulan Zhang, Mei Zhang, Alan M. Laties, Claire H. Mitchell
2005 Investigative Ophthalmology and Visual Science  
PURPOSE. Retinal ganglion cells are known to express ionotropic P2X 7 receptors for ATP. Stimulation of these receptors in other cells can elevate Ca 2ϩ and sometimes lead to cell death. This study asked whether P2X 7 receptor stimulation alters the Ca 2ϩ levels and viability of retinal ganglion cells. METHODS. P2X 7 agonists were applied to retinal ganglion cells from neonatal rats loaded with fura-2 to examine their effect on intracellular Ca 2ϩ levels. The effect of P2X 7 receptor
more » ... on cell viability was examined in rat retinal ganglion cells back-labeled with aminostilbamidine. RESULTS. The P2X 7 agonist benzoylbenzoyl adenosine triphosphate (BzATP) led to a large, sustained increase in Ca 2ϩ . BzATP was Ͼ100-fold more effective than ATP at raising intracellular Ca 2ϩ , when both agonists were applied at 10 M. The response to BzATP was enhanced threefold by removal of extracellular Mg 2ϩ , was dependent on extracellular Ca 2ϩ , 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 M. Cell death was prevented by the P2X 7 antagonists BBG and oxidized ATP, but not by 30 M 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 2ϩ channel blocker nifedipine attenuated cell death, suggesting excessive Ca 2ϩ influx contributes to the lethal effects of BzATP. CONCLUSION. Short-term stimulation of the P2X 7 receptor can raise Ca 2ϩ in rat retinal ganglion cells, whereas sustained stimulation of the receptor can kill them. (Invest Ophthalmol Vis Sci. 2005;46:2183-2191
doi:10.1167/iovs.05-0052 pmid:15914640 fatcat:udnvmqduvfbfpck5guj5o4scwu