Fig. 1

Channelrhodopsin-2 is a light-sensitive cation channel. A Channelrhodopsin-2 (ChR2) is rapidly opened by stimulation with blue (440–460 nm) light in an essentially nondesensitizing manner. ChR2 is permeable by multiple cations like Na⁺ and Ca²⁺ and enables strong and rapid membrane depolarization of the cell it is expressed in. B Multiple ChR2-expressing C. elegans strains exist, including but not limited to expressing in muscle cells (myo-3), cholinergic neurons (unc-17), and GABAergic neurons (unc-47). C The change in body length is often used as a readout of ChR2 activation (see B)