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Properties of voltage-gated potassium currents of microglia differentiated with granulocyte/macrophage
C Eder1, H G Fischer, U Hadding
1Institut für Neurophysiologie, Universität zu Köln, Germany.
Abstract:
Voltage-gated whole-cell currents were recorded from cultured microglial cells which had been developed in the presence of the macrophage/microglial growth factor granulocyte/macrophage colony-stimulating factor. Outward K+ currents (IK) were most prominent in these cells. IK could be activated at potentials more positive than -40 mV. Half-maximal activation of IK was achieved at -13.8 mV and half-maximal inactivation of IK was determined at -33.8 mV. The recovery of IK from inactivation was described by a time constant of 7.9 sec. For a tenfold change in extracellular K+ concentration the reversal potential of IK shifted by 54 mV. Extracellularly applied 10 mM tetraethylammonium chloride reduced IK by about 50%, while 5 mM 4-aminopyridine almost completely abolished IK. Several divalent cations (Ba2+, Cd2+, Co2+, Zn2+) reduced current amplitudes and shifted the activation curve of IK to more positive values. Charybdotoxin (IC50 = 1.14 nM) and noxiustoxin (IC50 = 0.89 nM) blocked IK in a concentration-dependent manner, whereas dendrotoxin and mast cell degranulating peptide had no effect on the current amplitudes. The outward K+ currents showed a frequency dependence when depolarizing pulses were applied at a frequency of 1 Hz. A frequency-independent outward current (IK') characterized by the same activation behavior as IK was detected. IK' was blocked completely by 10 nM charybdotoxin or by 10 nM noxiustoxin. In contrast to its effect on IK, 10 mM tetraethylammonium chloride did not reduce IK'.
Insights
This study characterizes outward potassium currents (IK) in cultured microglial cells, identifying specific blockers and their properties. These findings are crucial for understanding microglial cell function and potential therapeutic targets.
Area of Science:
- Neuroscience
- Cell Biology
- Immunology
Background:
- Microglial cells play critical roles in the central nervous system.
- Granulocyte/macrophage colony-stimulating factor (GM-CSF) influences microglial development.
- Understanding ion channel function in microglia is essential for neuroinflammation research.
Purpose of the Study:
- To characterize voltage-gated whole-cell outward potassium currents (IK) in cultured microglial cells.
- To investigate the properties and pharmacological profile of these currents.
- To identify specific modulators of microglial potassium channels.
Main Methods:
- Whole-cell patch-clamp electrophysiology was used to record currents from cultured microglial cells.
- Cells were developed in the presence of GM-CSF.
- Pharmacological agents including tetraethylammonium chloride, 4-aminopyridine, divalent cations, charybdotoxin, and noxiustoxin were applied.
Main Results:
- Outward potassium currents (IK) were prominent, activating at potentials more positive than -40 mV.
- Charybdotoxin and noxiustoxin potently blocked IK, while tetraethylammonium chloride partially inhibited it.
- A distinct frequency-independent outward current (IK') was identified, sensitive to charybdotoxin and noxiustoxin but not tetraethylammonium chloride.
Conclusions:
- Cultured microglial cells possess prominent voltage-gated outward potassium currents (IK).
- Specific potassium channel subtypes, likely sensitive to charybdotoxin and noxiustoxin, are involved in IK.
- These findings provide insights into the electrophysiological properties of microglia and potential targets for modulating their function.