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Updated: Jun 21, 2026
08:39
Whole-cell Patch-clamp Recordings for Electrophysiological Determination of Ion Selectivity in Channelrhodopsins
Published on: May 22, 2017
Channelrhodopsin-2 is a leaky proton pump.
Katrin Feldbauer1, Dirk Zimmermann, Verena Pintschovius
1Max-Planck-Institute of Biophysics, Max-von-Laue Strasse 3, 60438 Frankfurt, Germany.
Summary
Channelrhodopsin-2 (ChR2) is a light-gated ion channel crucial for neuroscience. This study reveals its unitary conductance and demonstrates its bifunctional nature as both an ion channel and a proton pump.
Area of Science:
- Neuroscience
- Biophysics
- Molecular Biology
Background:
- Channelrhodopsin-2 (ChR2) is a widely used optogenetic tool for controlling neural activity.
- The molecular mechanism and ion transport properties of ChR2 remain incompletely understood.
- Despite sequence homology to proton pumps, ChR2's function as a cation channel is well-established.
Purpose of the Study:
- To elucidate the molecular mechanism of Channelrhodopsin-2 (ChR2).
- To determine the unitary conductance and ion transport kinetics of ChR2.
- To investigate the potential proton pumping activity of ChR2.
Main Methods:
- Noise analysis to determine unitary conductance for various cations.
- Voltage-clamp electrophysiology to measure photocurrent kinetics.
- Time-resolved spectroscopy for kinetic analysis.
- Expression in HEK293 cells and reconstitution in lipid bilayers to assess proton pumping.
Main Results:
- Unitary conductance of ChR2 determined (e.g., 40 fS at 200 mM NaCl, -60 mV).
- Noise analysis kinetics align with photocurrent and spectroscopic data.
- Inward rectification explained by single-channel parameters.
- ChR2 demonstrated outward proton (H+) pumping activity in specific experimental setups.
Conclusions:
- ChR2 exhibits bifunctional properties, acting as both an ion channel and a proton pump.
- Its ion channel properties, including inward rectification, are consistent with single-channel parameters.
- ChR2 functions as a proton pump, aligning with other microbial rhodopsins, but possesses leak ion channel characteristics.
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