Figure 3.

ChR2(C128S) can be closed under steady-state blue illumination by the addition of a stoplight. (a) A HEK-293T cell expressing ChR2(C128S) was illuminated with the indicated pulse sequence under whole-cell voltage clamp at −70 mV. The initial pulse of red illumination was responsible for closing channels left open by the previous illumination cycle. Open channelrhodopsin passed a negative current. Intense orange light (300 W/cm², 594 nm) suppressed ∼95% of the photocurrent induced by moderate blue light (∼300 mW/cm², 488 nm). (b) Results of a kinetic simulation of the photocycle model in Fig. 2a using estimated rates. Each trace shows the expected population of the P520-conducting state at a different 488-nm illumination intensity (as in panel a). To see this figure in color, go online.