Phobos(CA) is an anion-selective channelrhodopsin that can be used as an optogenetic tool to inhibit neuron activity. It was generated by adding the C128A amino acid substitution to Phobos. This mutation slows off kinetics, resulting in Phobos(CA) behaving as a bistable channelrhodopsin; it is activated by a brief pulse of light to produce a prolonged photocurrent with a longer duration than the initiating pulse, resulting in a stable step in membrane potential, and it can be inactivated by a second light pulse of longer wavelength. Peak activation wavelength is 450nm, peak inactivation wavelength is 580nm (FBrf0237123). For detailed kinetic and spectral properties, see FBrf0237123. For a comparison of Phobos(CA) with other neuron inactivation tools, see FBrf0237123.