Figure 5. Effect of extracellular Mg²⁺ on glutamate-induced Ca²⁺ influx in isolated RGCs.

A, fura-2 ratio trace for an RGC, in HBSS containing 0.8 mm Mg²⁺, exposed to 10, 100 and 1000 μm glutamate (plus 10 μm glycine). Responses to lower glutamate concentrations (≤ 100 μm) were attenuated with Mg²⁺ present, but note that RGC still responded to 200 μm kainate (indicating AMPA/kainate-Rs were not inhibited by the extracellular Mg²⁺). B and C, representative trace (B) and mean normalized Ca²⁺ influx (change in [Ca²⁺]_i +1 s.d.) (C) for RGCs (n = 12) treated with 10 μm glutamate in the absence or presence of 0.8 mm Mg²⁺. D and E, fura-2 ratio traces illustrating effect of NMDA-R antagonist MK-801 (10 μm) (D) and AMPA/kainate-R antagonist NBQX (25 μm) (E) on RGC Ca²⁺ influx evoked by 1000 μm glutamate (plus 10 μm glycine) in HBSS containing 0.8 mm Mg²⁺. F, mean data (+1 s.d.) for effect of NMDA-R antagonists (hatched bars) and AMPA/kainate-R antagonist (filled bar) on glutamate-induced Ca²⁺ influx (normalized to initial response; dashed line). *P < 0.05, **P < 0.01, Friedman ANOVA, Tukey, compared to initial and recovery responses.