Ultra light-sensitive and fast neuronal activation with the Ca2+-permeable channelrhodopsin CatCh

In this Technical Report, Kleinlogel and colleagues created and characterized a new channelrhodopsin-2 mutant with an enhanced permeability to calcium. Dubbed CatCh (calcium translocating channelrhodopsin), this new variant's enhanced calcium permeability mediates an accelerated response time and voltage response that is ~70-fold more light sensitive than that of wild-type channelrhodopsin-2. The light-gated cation channel channelrhodopsin-2 (ChR2) has rapidly become an important tool in neuroscience, and its use is being considered in therapeutic interventions. Although wild-type and known variant ChR2s are able to drive light-activated spike trains, their use in potential clinical applications is limited by either low light sensitivity or slow channel kinetics. We present a new variant, calcium translocating channelrhodopsin (CatCh), which mediates an accelerated response time and a voltage response that is ∼70-fold more light sensitive than that of wild-type ChR2. CatCh's superior properties stem from its enhanced Ca2+ permeability. An increase in [Ca2+]i elevates the internal surface potential, facilitating activation of voltage-gated Na+ channels and indirectly increasing light sensitivity. Repolarization following light-stimulation is markedly accelerated by Ca2+-dependent BK channel activation. Our results demonstrate a previously unknown principle: shifting permeability from monovalent to divalent cations to increase sensitivity without compromising fast kinetics of neuronal activation. This paves the way for clinical use of light-gated channels.