Figure 3.

A summary of optogenetic actuators. Depolarizing channelrhodopsins, e.g., ChR2, open in response to light in the blue-green spectrum allowing positively-charged ions into the cell, raising the membrane potential and triggering the depolarization threshold. Conversely, inhibitory channels like Halorhodopsin (which pumps negatively-charged ions in) or Archaerhodopsin (which pumps protons out) hyperpolarize excitable membranes. Inhibitory channel activity is controlled by light in the green-red spectrum. The lower panel stylizes the effect on cell membrane potential by blue or orange pulses of light to depolarize, or hyperpolarize the cell. The two approaches can be combined to hyperpolarize, and then activate, the cell [95]. A number of reporter strategies discussed in this review can be integrated with stimulatory optical control [42,60,68,69,78,81,83,85,97].