Figure 5.

Ca²⁺ influx-induced downregulation of NMDA channel gating during activation of remote NMDA receptors could be overcome by a modest Na⁺ influx. A, An example of NMDA channel open probability (P_o; bin, 10 sec) recorded from neurons bathed with an extracellular solution containing 20 mm Na⁺ and 0.3 mm Ca²⁺. B, Summarized data (mean ± SEM) outlining the effects of remote NMDA receptor activation produced by the bath application of l-aspartate on P_o, mean open time (t_o), burst (B), cluster (C), and supercluster (S) lengths of NMDA channels recorded from neurons bathed with an extracellular solution containing 10 mm Na⁺ and 0.3 mm Ca²⁺ or 20 mm Na⁺ and 0.3 mm Ca²⁺ or 20 mm Na⁺ and 1.2 mm Ca²⁺. Values in parentheses indicate the number of patches tested. ^*p < 0.05; ^**p < 0.01 (Wilcoxon test). C, Examples of traces of [Na⁺]_i (top) and [Ca²⁺]_i (bottom) recorded in the soma region of neurons bathed with the extracellular solution containing 0.3 mm Ca²⁺ and 145 mm Na⁺ before and during l-aspartate (500 μm) application. D, Summarized data indicating changes (mean ± SEM) in [Na⁺]_i (top) and [Ca²⁺]_i (bottom) induced by the activation of NMDA receptors in neurons bathed with extracellular solutions containing 0.3 mm Ca²⁺ and 10, 20, or 145 mm Na⁺ in the absence and presence of monensin (10 μm) or Ca²⁺-ATPase inhibitor thapsigargin (0.1 μm); ^# p < 0.05; ^## p < 0.01 (Mann-Whitney test) in a comparison between groups as indicated. Values in parentheses indicate the number of neurons tested.