Stimulation of P2X7 receptors elevates Ca2+ and kills retinal ganglion cells

Abstract

PURPOSE. Retinal ganglion cells are known to express ionotropic P2X 7 receptors for ATP. Stimulation of these receptors in other cells can elevate Ca2+ and sometimes lead to cell death. This study asked whether P2X7 receptor stimulation alters the Ca2+ levels and viability of retinal ganglion cells. METHODS. P2X7 agonists were applied to retinal ganglion cells from neonatal rats loaded with fura-2 to examine their effect on intracellular Ca2+ levels. The effect of P2X7 receptor stimulation on cell viability was examined in rat retinal ganglion cells back-labeled with aminostilbamidine. RESULTS. The P2X7 agonist benzoylbenzoyl adenosine triphosphate (BzATP) led to a large, sustained increase in Ca2+. BzATP was > 100-fold more effective than ATP at raising intracellular Ca2+, when both agonists were applied at 10 μM. The response to BzATP was enhanced threefold by removal of extracellular Mg2+, 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 (LD50) of 35 μM. Cell death was prevented by the P2X 7 antagonists BBG and oxidized ATP, but not by 30 μM suramin, consistent with the actions of the P2X7 receptor. BzATP activated caspases in ganglion cells, but did not lead to membrane blebbing or increased permeability to Yo-Pro-1. The L-type Ca2+ channel blocker nifedipine attenuated cell death, suggesting excessive Ca2+ influx contributes to the lethal effects of BzATP. CONCLUSION. Short-term stimulation of the P2X7 receptor can raise Ca2+ in rat retinal ganglion cells, whereas sustained stimulation of the receptor can kill them. Copyright © Association for Research in Vision and Ophthalmology.