All-optic control and readout of membrane potential - analysis

VoltageRhodopsin is a mutant bacterial proton pump conjugated with a long Stokes shift FP in its terminal . The retinal core in the pump shifts its absorbance according to membrane voltage shifts or cross-membrane pH ratio changes. The FRET efficiency from FP to retinal core, thus, covaries with membrane voltage changes, given pH is stable. We control the N2A cell membrane voltage with red-light responsive VChR1, and readout the membrane voltage using blue fluorescence emission from a Cerulean-tagged VoltageRhodopsin. The experiment starts from a period of silence, then 10 pulses of red laser are delivered to stimulate the cell. As membrane voltage shifts, one could notice the bright fluorescence burst.