Transient, Consequential Increases in Extracellular Potassium Ions Accompany Channelrhodopsin2 Excitation

？ Multiple approaches reveal transient K+ elevations during ChR2 excitation ？ ChR2-mediated K+ elevations increase neuronal excitability and cFos expression ？ Neuronal effects of K+ are recapitulated with a model and in vivo ？ Increased K+ may contribute to astrocyte experiments employing ChR2 in viv