Hyperbaric pressure and increased susceptibility to glutamate toxicity in retinal ganglion cells in vitro.
OBJECTIVE
To investigate the effect of hyperbaric pressure on purified retinal ganglion cells (RGCs) and the additive effect of hyperbaric pressure on glutamate-induced RGC death.


METHODS
An RGC primary culture from 8-day-old Wistar rats was prepared and cultured in a hyperbaric chamber. The RGC survival rate under various pressure conditions and with 5 or 25 µM of glutamate stimulation was determined and compared with that of RGCs under isobaric conditions. First, RGCs were cultured at atmospheric pressure (0 mmHg) and under hyperbaric pressure (+30 and +90 mmHg, with pressure fluctuations varying from 0 to +30 or +60 mmHg). Next, RGCs were cultured at +15, +30, and +90 mmHg with the addition of 5 or 25 µM of glutamate. The effects of N-Methyl-D-aspartic acid (NMDA) and 2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl)propanoic acid (AMPA)/kainate receptor antagonists, MK-801, and 6,7-dinitroquinoxaline-2,3-dione (DNQX), on cell survival were assessed. Additionally, types of cell death and the induction of Bcl-2-associated X protein (BAX) leading to apoptosis were studied under hyperbaric pressure conditions and/or with 5 µM of glutamate.


RESULTS
RGC death was not induced under increasing or fluctuating pressure conditions. RGC death was induced by 25 µM of glutamate and increased as pressure increased. RGC death was not induced by 5 µM of glutamate but was induced by and increased with increasing pressure. MK-801 and DNQX significantly reduced glutamate-induced RGC death, and DNQX was more effective than MK-801. Under hyperbaric pressure conditions, the addition of 5 µM of glutamate resulted in the induction of apoptosis and BAX, which did not occur under hyperbaric pressure conditions or with the addition of glutamate alone.


CONCLUSIONS
In a rat RGC culture, hyperbaric pressure alone did not induce RGC death but increased RGC susceptibility to glutamate toxicity, which may be of relevance to ocular diseases with pressure-induced RGC death.
Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan.
Makoto
M
Aihara
Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan.
Yi-Ning
YN
Chen
Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan.
Saiko
S
Uchida
Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan.
Mao
M
Nakayama
Department of Ophthalmology, University of Tokyo School of Medicine, Tokyo, Japan.
Makoto
M
Araie
D000818:Animals; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018698:Glutamic Acid / Q000633:toxicity*; D011312:Pressure; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D013312:Stress, Physiological / Q000187:drug effects; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D011810:Quinoxalines; D017470:Receptors, Glutamate; D051028:bcl-2-Associated X Protein; D018698:Glutamic Acid; C056723:FG 9041; D016291:Dizocilpine Maleate