Protective effect of nilvadipine against glutamate neurotoxicity in purified retinal ganglion cells

Abstract

We determined the effect of nilvadipine, a dihydropyridine-type calcium channel blocker, in preventing glutamate neurotoxicity in purified retinal ganglion cells (RGCs). RGCs were purified from dissociated rat retinal cells (postnatal days 6–8), using a modified two-step panning method, and cultured in serum-free medium containing neurotrophic factors and forskolin. RGC survival after exposure to glutamate (25 μM) with nilvadipine or other calcium channel blockers was measured by calcein-acetoxymethyl ester staining after 3 days in culture. Changes in the level of intracellular Ca 2+ ([Ca 2+] i) were measured with fura-2 fluorescence. Induction of apoptosis was evaluated using the TDT-dUTP terminal nick-end labeling technique. The neurotoxic effects of low doses of glutamate were blocked by a specific α-amino-3-dihydro-5-methylisoxazole-4-propionate-kainate receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (20 μM). Simultaneous application of nilvadipine (1–100 nM) with glutamate protected against glutamate neurotoxicity in a dose-dependent manner. Calcium-imaging experiments showed that the glutamate-evoked [Ca 2+] i increase was significantly blocked by nilvadipine ( P<0.001), but not nifedipine and diltiazem, in about 50% of RGCs. In addition, the application of nilvadipine significantly reduced glutamate-induced apoptosis ( P<0.001). These findings suggest that nilvadipine may partly inhibit glutamate-induced apoptotic cell death by blocking calcium influx via voltage-dependent calcium channels in purified RGCs.