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Membrane properties of ameboid microglial cells in the corpus callosum slice from early postnatal mice
J Brockhaus1, S Ilschner, R B Banati
1Department of Neurobiology, University of Heidelberg, Germany.
Abstract:
Microglial cells in culture are distinct from neurons, macroglial cells, and macrophages of tissues other than brain with respect to their membrane current pattern. To assess these cells in the intact tissue, we have applied the patch-clamp technique to study membrane currents in microglial cells from acute, whole brain slices of 6-9-d-old mice in an area of microglial cell invasion, the cingulum. As strategies to identify microglial cells prior to or after recording, we used binding and incorporation of Dil-acetylated low-density lipoproteins, binding of fluorescein isothiocyanate-coupled IgG via microglial Fc-receptors, and ultrastructural characterization. As observed previously for cultured microglial cells, depolarizing voltage steps activate only minute if any membrane currents, while hyperpolarizing voltage steps induced large inward currents. These currents exhibited properties of the inwardly rectifying K+ channel in that the reversal potential depended on the transmembrane K+ gradient, inactivation time constants decreased with hyperpolarization, and the current was blocked by tetraethylammonium (50 mM). This study represents the first attempt to assess microglial cells in situ using electrophysiological methods. It opens the possibility to address questions related to the function of microglial cells in the intact CNS.
Insights
This study electrophysiologically characterizes microglial cells in intact brain tissue for the first time. In situ, these immune cells exhibit inward potassium currents, similar to those seen in cell cultures.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglial cells, the resident immune cells of the central nervous system (CNS), exhibit distinct membrane current patterns compared to other cell types in culture.
- Understanding microglial cell electrophysiology in their native tissue environment is crucial for elucidating their function in the intact CNS.
Purpose of the Study:
- To investigate the electrophysiological properties of microglial cells within intact brain tissue.
- To compare in situ microglial cell membrane currents with those previously observed in cultured cells.
Main Methods:
- Utilized the patch-clamp technique on acute whole brain slices from young mice (6-9 days old).
- Focused on an area of microglial cell invasion (cingulum) to ensure adequate cell numbers.
- Employed multiple strategies for microglial cell identification, including Dil-acetylated LDL uptake, Fc-receptor binding (FITC-coupled IgG), and ultrastructural analysis.
Main Results:
- In situ microglial cells showed minimal current activation upon depolarizing voltage steps.
- Hyperpolarizing voltage steps elicited large inward currents.
- These inward currents demonstrated characteristics of inwardly rectifying potassium (K+) channels, including dependence on the potassium gradient, voltage-dependent inactivation, and block by tetraethylammonium.
Conclusions:
- This study provides the first electrophysiological assessment of microglial cells in situ.
- The findings confirm similarities between cultured and in situ microglial membrane current patterns, specifically inward rectification.
- This work establishes a foundation for future research into microglial cell function within the intact central nervous system.