Figure 1.

Genetic reporters of pH detect intracellular pH changes during epileptiform activity. (A) A schematic of the experimental setup. A hippocampal pyramidal neuron transfected with a genetically encoded pH indicator was imaged using either two-photon or single-photon confocal microscopy. This allowed dynamic measurement of intracellular pH. A whole-cell patch recording from a neighboring neuron (cell somata <200 μm apart) provided simultaneous readout of seizure activity within the hippocampal slice. (B) A confocal image of a CA3 pyramidal neuron expressing the pH indicator E²GFP. The dashed rectangle demarcates the region of interest used to estimate intracellular pH. (C) Dynamic intracellular pH measurements imaged from the neuron in “b” (lower trace). A neuron in close proximity was whole-cell patched and the membrane potential recorded over time in current clamp mode (upper trace). Perfusion of the slice with 0 Mg²⁺ induced periods of epileptiform activity characterized by membrane depolarization and high frequency firing, the onset of which is depicted by red dashed lines. Note the marked acidic shifts in pH that are associated with epileptiform activity. Even brief periods of activity were associated with detectable acidic transients (indicated by asterisks).