Stabilized Ion Selectivity Corrects Activation Drift in Kalium Channelrhodopsins

Area of Science:

• Neuroscience
• Optogenetics
• Molecular Biology

Background:

• Optogenetic inhibition of neuronal activity is crucial for neuroscience research.
• Potassium-selective channelrhodopsins (KCRs) are promising for neuronal silencing but often suffer from ion selectivity shifts under prolonged illumination, limiting their efficacy.
• This ion selectivity shift can lead to unintended neuronal excitation, hindering reliable circuit silencing.

Purpose of the Study:

• To identify and characterize KCR variants with stable ion selectivity for reliable optogenetic neuronal inhibition.
• To evaluate the performance of KCR variants in silencing neural circuits across different species and conditions.
• To establish improved design criteria for next-generation optogenetic inhibitory tools.

Main Methods:

• Behavioral and electrophysiological analyses were performed in model organisms, including Drosophila and Caenorhabditis elegans.
• The ion selectivity (K+/Na+ permeability ratio) and its stability over time under illumination were assessed for various KCR variants.
• In vivo inhibition efficacy of KCR variants was tested across different cell types and illumination conditions.

Main Results:

• The KCR1-C29D mutant demonstrated a high and exceptionally stable K+/Na+ permeability ratio during illumination compared to other tested KCR variants.
• Unlike other variants that often induced excitatory responses, KCR1-C29D consistently achieved robust in vivo neuronal inhibition.
• The stability of ion selectivity was identified as a critical factor determining the effectiveness of KCRs for silencing neural circuits.

Conclusions:

• KCR1-C29D is a superior and reliable optogenetic tool for neuronal inhibition due to its stable ion selectivity.
• This study addresses a significant limitation in KCR optogenetics, providing a dependable method for silencing neural circuits.
• The findings emphasize the importance of ion selectivity stability in designing effective future optogenetic tools.