Figure 7. Extracellular Na⁺‐dependency of resting membrane potential.

A, membrane hyperpolarization in response to bath‐applied low Na⁺‐containing saline (NaCl substituted by an equimolar concentration of NMDG‐Cl) in a spontaneously spiking (bursting) CC at RMP. Note the reversibility of the effect with AP resuming upon re‐administration of a standard extracellular Na⁺ concentration. B, pooled data of low extracellular Na⁺‐induced RMP changes as a function of the firing discharge pattern. Representative chart recordings of low Na⁺ (NMDG‐replaced)‐elicited membrane potential changes are plotted above each group of cells (left panel for regular spiking cells, middle panel for bursting cells and right panel for silent cells). The mean value of resting membrane potential was −39.8 ± 3.9 mV in control saline versus −54.5 ± 11.9 mV in low Na⁺‐containing saline for cells with regular firing (n = 10 cells, P < 0.05 ( = 0.0137), Wilcoxon matched‐pairs signed‐rank test), −44.2 ± 5.9 mV in control saline versus −50.8 ± 8.2 mV in low Na⁺‐containing saline for cells with burst firing pattern (n = 10 cells, P < 0.05 ( = 0.0273), Wilcoxon matched‐pairs signed‐rank test) and −52.2 ± 6.1 mV in control saline versus −59.9 ± 10.7 mV in low Na⁺‐containing saline for silent cells (n = 10 cells, P > 0.05 ( = 0.1934), Wilcoxon matched‐pairs signed‐rank test). [Color figure can be viewed at wileyonlinelibrary.com]