UASt regulatory sequences drive expression of 'CapChR2' (Coog\ChR carrying amino acid replacements S43D, L112C, T139C and N238E). The mutations in CapChR2 were designed to improve Ca[2+] selectivity. In cell culture, when activated by blue light, CapChR2 behaves as a calcium-permeable channelrhodopsin, showing reduced Na[+] and H[+] conductance along with strongly improved Ca[2+] permeation at negative voltage and low extracellular Ca[2+] concentrations. In transgenic animals, a robust increase in Ca[2+] permeability is seen upon blue light exposure.