Membrane potential of cells expressing different ChR variants.

<p>The light stimulus (top) was identical to Fig. 5. The current traces from Fig. 5 are translated into membrane voltage according to the membrane equation −<i>C V</i>’(<i>t</i>) = (<i>V</i>(<i>t</i>) − <i>V</i>_rest)/<i>R</i>+<i>k</i>_exp <i>g</i>_ChR (<i>V</i>(<i>t</i>) − <i>V</i>_reverse) with <i>C</i> = 6 pF, <i>R</i> = 5 GOhm, <i>V</i>_rest = −55 mV, <i>V</i>_reverse = 0 mV, and <i>g</i>_ChR = (<i>g</i>₁ <i>O</i>₁+<i>g</i>₂ <i>O</i>₂). <b>A</b>: Membrane potential fluctuations caused by currents carried by Variant A (Fig. 5B) and Variant B (Fig. 5C). <b>B</b>: Effect of different expression levels <i>k</i>_exp on membrane potential modulation. <b>C</b>: Expressing Variant A and Variant B together in a single cell, at moderate expression levels, leads to modulation of membrane potential over 7 orders of magnitude. In each panel, we show the hypothetical saturation level of the cell (−25 mV). Depolarization beyond this level is indicated by dimly printed voltage traces.