Elevation of intracellular Ca2+ concentration induced by hypoxia in retinal ganglion cells

Purpose: To analyze the mechanism of hypoxia-induced changes of the intracellular Ca2+ concentration ([Ca2+](i)) in retinal ganglion cells (RGCs). Methods: Fluo-3 was applied to the cut edge of the optic nerve of 6-week-old rats. The retina was sliced, and the Ca images were captured. A hypoxic condition was created by superfusing the retinal slice with an oxygen/glucose-deprived solution. Results: The retrograde staining method filled the RGCs selectively. Fifteen minutes of hypoxic conditions induced an increase in [Ca2+]i in the RGCs (Delta 0.13 +/- 0.03, n = 23). Application of 60 mu M DL-2-amino5-phosphonovaleric acid partially blocked the hypoxia-induced [Ca2+], increase in dendrites (Delta 0.03 +/- 0.02, n = 4, P < 0.05) but not in the somata (Delta 0.12 Delta 0.02, n = 9). The RGC dendrites showed a further increase in [Ca2+](i) after being switched back to an oxygenated solution (Delta 0.14 +/- 0.04, n = 4). Neither 6-cyano-7-nitroq uinoxaline-2,3-dione disodium, DL-threo-beta-benzyloxyaspartate, nifedipine, nor bepridil inhibited the hypoxia-induced [Ca2+]i increase. A Ca2+ free superfusion prevented the hypoxia-induced [Ca2+](i) increase in the somata (Delta 0.07 +/- 0.02, n = 5, P < 0.05) but not in the dendrites (Delta 0.16 +/- 0.005, n = 4). Conclusions: The mechanism of the hypoxia-induced increase in [Ca2+](i) differs between somata and dendrites. The N-methyl-D-aspartate channel of dendrites seems to be the main route of Ca2+ influx.