UASt regulatory sequences drive expression of 'CapChR1' (Crei\ChR2 carrying amino acid replacements S63D, L132C, T159C and N258E). The mutations in CapChR1 were designed to improve Ca[2+] selectivity. In cell culture, when activated by blue light, CapChR1 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 (although CapChR1 does not trigger Ca[2+] influx to the same extent as the CapChR2 calcium-permeable channelrhodopsin). However, in transgenic animals, only a small increase in Ca[2+] permeability is seen upon blue light exposure.