Figure 1.

Schematic of channelrhodopsin-2 (ChR2). ChR2 expression does not affect the resting membrane potential because the gate is closed without blue light. When ChR2 is illuminated with blue light, the gate is opened, and it functions as a nonselective cation channel, resulting in the depolarization of ChR2-expressing neurons mainly due to Na⁺ entry. If the Na⁺ entry is large enough to reach the threshold, voltage-gated Na⁺ channels open, evoking an action potential.