Figure 4.

Alkaline transients in astrocytes during epileptiform activity are mediated by depolarization and the sodium-bicarbonate cotransporter NBCe1. A, Dual whole-cell current-clamp recording from a pair of CA3 pyramidal neurons (somata <200 μm apart) during 0 Mg²⁺-induced epileptiform activity. Dashed line indicates onset of a SLE. The membrane potential of the two neurons was highly synchronous, as indicated by the tight correlation in the cells' membrane potentials (r = 0.92, Pearson correlation). Action potential generation in response to somatic current injection (insets) confirmed both cells were neuronal. B, Dual whole-cell current-clamp recording from a pyramidal neuron (black trace) and a nearby astrocyte (red trace; somata <200 μm apart). Note that the astrocytic membrane potential depolarization during the SLE is tightly correlated with neuronal membrane potential (r = 0.82, Pearson correlation). Response to somatic current injection confirmed the identity of the cells (insets). C, Population data revealed a high correlation in the membrane potential between pyramidal neurons (r = 0.91 ± 0.01, Pearson correlation), and between pyramidal neurons and astrocytes (r = 0.80 ± 0.02, Pearson correlation) during SLEs. D, Under control conditions intracellular pH imaging with E²GFP (red trace) revealed transient alkalinizations that were associated with 0 Mg²⁺-induced epileptiform activity, as monitored from a nearby pyramidal neuron (black trace). E, Bath application of the selective Na⁺/HCO₃⁻ cotransporter blocker S0859 (50 μm) to the same cells as in D, resulted in a marked attenuation of the astrocytic alkalinizations. F, Population data demonstrate that S0859 blocks the astrocytic alkalinizations and eliminates the correlation between SLE duration and the size of the alkaline shift (r = 0.4289, p = 0.08 vs r = 0.69, p < 0.0001, Pearson correlation). G, For SLEs of comparable duration (<35 s duration), S0859 significantly reduced the peak change in astrocytic pH_i associated with 0 Mg²⁺-induced SLEs (left) and 0 Cl⁻-induced SLEs (center). Low HCO₃⁻ ACSF also reduced SLE-associated astrocytic alkaline shifts in 0 Cl⁻ ACSF (right). *p < 0.05, **p < 0.01, ***p < 0.0001, t test.