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Astrocytic inwardly rectifying potassium currents are dependent on external sodium ions
C B Ransom1, H Sontheimer, D Janigro
1Neurobiology Research Center, University of Alabama School of Medicine, Birmingham 35294, USA.
Journal of Neurophysiology
|July 1, 1996
Summary
Two astrocyte subtypes were identified based on ion channel expression. Inwardly rectifying potassium (Kir) channel conductance in glial cells is modulated by external sodium, independent of permeation or blockade.
Area of Science:
- Neuroscience
- Cell Biology
- Physiology
Background:
- Astrocytes play crucial roles in central nervous system function.
- Ion channels are critical for astrocyte electrophysiological properties.
- Distinct astrocyte subtypes may exhibit unique channel expression profiles.
Purpose of the Study:
- To identify and characterize astrocyte subtypes based on ion channel expression.
- To investigate the role of external sodium on astrocyte ion channel function, particularly inwardly rectifying potassium (Kir) channels.
Main Methods:
- Primary astrocyte cultures from rat spinal cord and hippocampus.
- Whole-cell patch-clamp electrophysiology.
- Manipulation of external sodium concentrations to assess ion channel activity.
Main Results:
- Two astrocyte populations were distinguished: one with voltage-activated Na+ currents and another with prominent inwardly rectifying K+ (Kir) currents.
- Astrocytes with Kir currents showed increased input resistance and reduced current amplitude upon external sodium removal, suggesting sodium-dependent conductance.
- External sodium removal did not affect outward potassium currents in Na+-current expressing astrocytes.
Conclusions:
- Glial inwardly rectifying K+ (Kir) channel conductance is dependent on external sodium ions.
- This sodium dependence occurs through a mechanism not involving direct sodium permeation or blockade of the Kir channels.
- Identified astrocyte subtypes possess distinct electrophysiological properties related to ion channel expression.