Figure 1. Rhodopsins can be used as actuators and sensors in optogenetics.
Actuators transport ions across the membrane to activate or repress neuronal activity. ChRs transport positively charged ions into the cell, while proton-pumping rhodopsins (PPRs) move protons out of the cell. In the ideal case, engineered rhodopsin sensors emit light as fluorescence in the farred in a voltage-dependent fashion.