Channelrhodopsin-2, a directly light-gated cation-selective membrane channel

Proc Natl Acad Sci U S A. 2003 Nov 25;100(24):13940-5. doi: 10.1073/pnas.1936192100. Epub 2003 Nov 13.


Microbial-type rhodopsins are found in archaea, prokaryotes, and eukaryotes. Some of them represent membrane ion transport proteins such as bacteriorhodopsin, a light-driven proton pump, or channelrhodopsin-1 (ChR1), a recently identified light-gated proton channel from the green alga Chlamydomonas reinhardtii. ChR1 and ChR2, a related microbial-type rhodopsin from C. reinhardtii, were shown to be involved in generation of photocurrents of this green alga. We demonstrate by functional expression, both in oocytes of Xenopus laevis and mammalian cells, that ChR2 is a directly light-switched cation-selective ion channel. This channel opens rapidly after absorption of a photon to generate a large permeability for monovalent and divalent cations. ChR2 desensitizes in continuous light to a smaller steady-state conductance. Recovery from desensitization is accelerated by extracellular H+ and negative membrane potential, whereas closing of the ChR2 ion channel is decelerated by intracellular H+. ChR2 is expressed mainly in C. reinhardtii under low-light conditions, suggesting involvement in photoreception in dark-adapted cells. The predicted seven-transmembrane alpha helices of ChR2 are characteristic for G protein-coupled receptors but reflect a different motif for a cation-selective ion channel. Finally, we demonstrate that ChR2 may be used to depolarize small or large cells, simply by illumination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algal Proteins / chemistry
  • Algal Proteins / genetics
  • Algal Proteins / metabolism*
  • Animals
  • Cations / metabolism
  • Cell Line
  • Chlamydomonas reinhardtii / genetics
  • Chlamydomonas reinhardtii / metabolism
  • Cricetinae
  • Female
  • Humans
  • Hydrogen-Ion Concentration
  • In Vitro Techniques
  • Ion Channel Gating / radiation effects
  • Ion Channels / chemistry
  • Ion Channels / genetics
  • Ion Channels / metabolism*
  • Light
  • Membrane Potentials
  • Oocytes / metabolism
  • Photobiology
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Rhodopsin / chemistry
  • Rhodopsin / genetics
  • Rhodopsin / metabolism*
  • Xenopus laevis


  • Algal Proteins
  • Cations
  • Ion Channels
  • Protozoan Proteins
  • Recombinant Proteins
  • Rhodopsin