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Sci Rep. 2015 Oct 7;5:14807. doi: 10.1038/srep14807.

An improved chloride-conducting channelrhodopsin for light-induced inhibition of neuronal activity in vivo.

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Institute for Biology, Experimental Biophysics, Humboldt-Universität zu Berlin, D-10115 Berlin, Germany.
Center for Neural Circuits and Behavior, University of California San Diego, La Jolla, CA 92093-0634, USA.
Howard Hughes Medical Institute, University of California San Diego, La Jolla, CA 92093-0634, USA.
Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, D-20251 Hamburg, Germany.


Channelrhodopsins are light-gated cation channels that have been widely used for optogenetic stimulation of electrically excitable cells. Replacement of a glutamic acid in the central gate with a positively charged amino acid residue reverses the ion selectivity and produces chloride-conducting ChRs (ChloCs). Expressed in neurons, published ChloCs produced a strong shunting effect but also a small, yet significant depolarization from the resting potential. Depending on the state of the neuron, the net result of illumination might therefore be inhibitory or excitatory with respect to action potential generation. Here we report two additional amino acid substitutions that significantly shift the reversal potential of improved ChloC (iChloC) to the reversal potential of endogenous GABAA receptors. As a result, light-evoked membrane depolarization was strongly reduced and spike initiation after current injection or synaptic stimulation was reliably inhibited in iChloC-transfected neurons in vitro. In the primary visual cortex of anesthetized mice, activation of iChloC suppressed spiking activity evoked by visual stimulation. Due to its high operational light sensitivity, iChloC makes it possible to inhibit neurons in a large volume of brain tissue from a small, point-like light source.

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