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Related Experiment Videos

K+ waves in brain cortex visualized using a long-wavelength K+-sensing fluorescent indicator.

Prashant Padmawar1, Xiaoming Yao, Orin Bloch

  • 1Department of Medicine, Cardiovascular Research Institute, 1246 Health Sciences East Tower, University of California, San Francisco, California 94143, USA.

Nature Methods
|November 10, 2005
PubMed
Summary

We developed TAC-Red, a novel sensor for potassium (K+), which visualizes K+ dynamics in the brain. This sensor revealed that Aquaporin-4 (AQP4) is crucial for K+ reuptake in astrocytes.

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Area of Science:

  • Neuroscience
  • Biochemistry
  • Chemical Biology

Background:

  • Potassium (K+) homeostasis is critical for neuronal function.
  • Monitoring extracellular K+ dynamics in real-time is essential for understanding brain activity.
  • Existing methods for K+ sensing have limitations in sensitivity, selectivity, or application in vivo.

Purpose of the Study:

  • To develop a novel, water-soluble, long-wavelength fluorescent sensor for K+.
  • To visualize and quantify K+ dynamics in the brain during physiological events.
  • To investigate the role of Aquaporin-4 (AQP4) in K+ regulation in astrocytes.

Main Methods:

  • Synthesis of TAC-Red, a triazacryptand-conjugated xanthylium derivative.
  • Characterization of TAC-Red's spectral properties and K+ binding affinity.

Related Experiment Videos

  • In vivo imaging of K+ waves in mouse brain cortex using TAC-Red during spreading depression.
  • Measurement of K+ release and reuptake kinetics.
  • Assessment of K+ reuptake in wild-type and AQP4-knockout mice.

    • Main Results:

    • TAC-Red exhibits a 14-fold fluorescence increase with K+ (0-50 mM) and high K+/Na+ selectivity (>30).
    • Visualized K+ waves in mouse brain cortex with a velocity of 4.4 ± 0.5 mm/min.
    • Determined K+ release and reuptake half-times of 12 ± 2 s and 32 ± 4 s, respectively.
    • AQP4 deletion in mice resulted in a twofold slowing of K+ reuptake.

    Conclusions:

    • TAC-Red is a sensitive and selective fluorescent sensor for monitoring K+ dynamics in the brain.
    • The study provides real-time visualization of K+ waves during spreading depression in vivo.
    • Results suggest a significant role for AQP4 in astrocytic K+ uptake and clearance from the extracellular space.