Fig. 5.

Ca²⁺ entry and cell death are much higher after NMDAR activation than after depolarization-evoked VGCC activation. The traces show the dose–response of cytosolic Ca²⁺ in cultured hippocampal neurons to increasing concentrations of NMDA (μM, as indicated) in comparison with the strong depolarization-induced Ca²⁺ entry via VGCCs (90 mM K⁺ plus 1 μM Bay K 8644 (a calcium channel activator) in 10 mM Ca²⁺ saline). The relative death rates at 24 h are given in parentheses. Free Ca²⁺ was measured using the low-affinity ratiometric probe fura-4FF. Near-maximal VGCC activation and NMDA at the lowest dose used (10 μM) elicit similarly small Ca²⁺ elevations and minimal cell death.