Transient, Consequential Increases in Extracellular Potassium Ions Accompany Channelrhodopsin2 Excitation (Cell Reports)

Using multiple approaches, Octeau et al. discover that optogenetic excitation of ChR2-expressing cells leads to significant transient extracellular potassium ion elevations that increase neuronal excitability and immediate early gene expression in neurons following in vivo stimulation.