title: Two-photon excitation of channelrhodopsin-2 at saturation.
abstract: We demonstrate that channelrhodopsin-2 (CR), a light-gated ion channel that is conventionally activated by using visible-light excitation, can also be activated by using IR two-photon excitation (TPE). An empirical estimate of CR's two-photon absorption cross-section at lambda = 920 nm is presented, with a value (260 +/- 20 GM) indicating that TPE stimulation of CR photocurrents is not typically limited by intrinsic molecular excitability [1 GM = 10(-50)(cm4 s)/photon]. By using direct physiological measurements of CR photocurrents and a model of ground-state depletion, we evaluate how saturation of CR's current-conducting state influences the spatial resolution of focused TPE photostimulation, and how photocurrents stimulated by using low-power scanning TPE temporally summate. We show that TPE, like visible-light excitation, can be used to stimulate action potentials in cultured CR-expressing neurons.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
authors.forename: John Peter
authors.initials: JP
authors.lastname: Rickgauer
authors.forename: David W
authors.initials: DW
authors.lastname: Tank
mesh_terms: D002460:Cell Line; D055724:Electrophysiological Phenomena; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D017785:Photons; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism*
chemical_list: D007473:Ion Channels; D012243:Rhodopsin
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