EFFECT OF GLUCOSE DEPRIVATION AND ACUTE GLUTAMATE EXPOSURE IN CULTURED RETINAL CELLS

The relationship between bioenergetics and the glutamate system was an alyzed in a neuronal model of retinal cells in culture, submitted to g lucose deprivation and exposed to glutamate for 2 h, and compared with exposure to glutamate in the presence of glucose. Under glucose depri vation, a reduction (about 1.1-fold) in the energy charge of the cells occurred, probably as a result of a decrement (by about 75%) in the c ellular redox efficacy, as determined by the 3-(4,5-dimethylthiazol-2- yl)-2,5-diphenyl tetrazolium bromide (MTT) test. In the absence of glu cose, exposure of retinal cells to 10 mu M glutamate potentiated the r eduction in the energy charge (by about 1.2-fold) and induced a signif icant increase in the uptake of Ca-45(2+) by th, cells (1.3-fold), alt hough no significant changes were observed in the presence of glucose. Under glucose deprivation, 100 mu M glutamate caused an irreversible cell membrane damage, as shown by the significant increase in lactate dehydrogenase (LDH) leakage (about 1.8-fold). A significant increase i n membrane depolarization, measured by the reduction of [H-3]tetraphen ylphosphonium(+) ([H-3]TPP+) uptake, was also observed after glutamate exposure in the absence of glucose. In the presence of glucose, high glutamate concentrations (10 mM) induced a major increase in Ca2+ entr y into the cells and membrane depolarization, without affecting the en ergy charge or cell survival. In contrast, in the absence of glucose, 10 mM glutamate did not alter Ca2+ accumulation by the cells and a sma ller decrease in membrane potential occurred, as compared to 100 mu M glutamate exposure. Data shown in this study suggest that during a pro longed (2 h) and acute exposure to high glutamate (10 mM), under gluco se deprivation conditions, the neuronal systems have ''adaptive'' mech anisms that allow the survival of cells. These findings may have impli cations in neuronal degeneration occurring during brain ischemia. (C) 1998 Academic Press.