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Related Experiment Video

Updated: Feb 2, 2026

Imaging Membrane Potential with Two Types of Genetically Encoded Fluorescent Voltage Sensors
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Fast, in vivo voltage imaging using a red fluorescent indicator.

Madhuvanthi Kannan1,2,3, Ganesh Vasan1,2,3, Cheng Huang4

  • 1The John B. Pierce Laboratory, New Haven, CT, USA.

Nature Methods
|November 14, 2018
PubMed
Summary

Researchers developed VARNAM, a new red fluorescent voltage indicator for brain imaging. This tool enables high-speed, cell-type-specific imaging in vivo and in vitro, advancing neuroscience research.

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Area of Science:

  • Neuroscience
  • Optical Imaging
  • Molecular Biology

Background:

  • Genetically encoded voltage indicators (GEVIs) are crucial for brain-wide functional imaging.
  • Existing GEVIs have limitations in temporal resolution and spectral compatibility.
  • There is a need for GEVIs suitable for high-speed multispectral imaging.

Purpose of the Study:

  • To develop a novel GEVI with enhanced performance for high-speed multispectral imaging.
  • To create a red-shifted GEVI compatible with existing optical tools.
  • To validate the efficacy of the new GEVI in various biological preparations.

Main Methods:

  • A high-throughput screening strategy was employed.
  • A fusion protein, VARNAM, was engineered combining a fast opsin and mRuby3 fluorophore.
  • In vivo and in vitro experiments were conducted using acute brain slices, live Drosophila, and freely behaving mice.

Main Results:

  • VARNAM demonstrated high sensitivity to voltage changes, including subthreshold potentials.
  • It is compatible with modest illumination intensities, enabling in vivo use.
  • VARNAM facilitated dual-color spike imaging and all-optical electrophysiology.
  • VARNAM successfully resolved neuronal activity in brain slices and cortical/hippocampal rhythms in mice.

Conclusions:

  • VARNAM expands the capabilities of optical tools for neuroscience.
  • It enables high-speed, cell-type-specific, multispectral functional imaging in vivo.
  • VARNAM is a valuable addition to the neuroscience research toolkit, particularly for advanced optical electrophysiology.