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Properties of voltage-gated currents of microglia developed using macrophage colony-stimulating factor
C Eder1, H G Fischer, U Hadding
1Institut für Neurophysiologie, Universität zu Köln, Germany.
Abstract:
Microglia were isolated from a murine neonatal brain cell culture in which their development had been stimulated by supplementation with the macrophage/microglial growth factor macrophage colony-stimulating factor (M-CSF). Using the whole-cell configuration of the patch-clamp technique, voltage-gated membrane currents were recorded from these microglial cells. Hyperpolarization induced inward rectifying K+ currents, as described for microglia from untreated cultures. These currents activated negative to the K+ equilibrium potential and, with a strong hyperpolarization, displayed time-dependent inactivation. The inactivation was abolished when extracellular NaCl was replaced by N-methyl-D-glucamine (NMG), thereby indicating a partial block of this K+ conductance by Na+. Inward rectifying currents were also blocked by extracellularly applied Cs+ or Ba2+. They were slightly diminished following treatment with extracellular tetraethylammonium chloride (TEA) but were not affected by 4-aminopyridine (4-AP). Upon long lasting depolarizing voltage pulses to potentials positive to 0 mV, the cells exhibited a slowly activating H+ current which could be reduced by application of inorganic polyvalent cations (Ba2+, Cd2+, Co2+, La3+, Ni2+, Zn2+) as well as by 4-AP or TEA. Based on their kinetics and pharmacological characteristics, both currents detected on M-CSF-grown microglia are suggested to correspond to the inward rectifier and the H+ current of macrophages.
Insights
Macrophage colony-stimulating factor (M-CSF) promotes microglial development, revealing distinct inward rectifier K+ and H+ currents. These currents exhibit unique properties and pharmacological profiles, suggesting similarities to macrophage currents.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia, the resident immune cells of the central nervous system, play crucial roles in brain development and disease.
- Macrophage colony-stimulating factor (M-CSF) is a key growth factor influencing microglial proliferation and differentiation.
- Understanding microglial ion channel function is essential for elucidating their physiological roles.
Purpose of the Study:
- To characterize the voltage-gated membrane currents in microglia cultured with M-CSF.
- To investigate the properties and pharmacological sensitivities of these currents.
- To compare the identified currents with those found in macrophages.
Main Methods:
- Isolation of microglia from murine neonatal brain cell cultures.
- Stimulation of microglial development using M-CSF.
- Whole-cell patch-clamp technique to record voltage-gated membrane currents.
- Pharmacological assessment using various ion channel blockers (e.g., Cs+, Ba2+, TEA, 4-AP) and ionic substitutions (NaCl replaced by NMG).
Main Results:
- Hyperpolarization induced inward rectifying K+ currents, exhibiting time-dependent inactivation abolished by Na+ removal.
- Inward rectifying currents were sensitive to Cs+, Ba2+, and slightly to TEA, but not 4-AP.
- Depolarizing pulses revealed a slowly activating H+ current, inhibited by polyvalent cations (Ba2+, Cd2+, Co2+, La3+, Ni2+, Zn2+) and 4-AP or TEA.
Conclusions:
- M-CSF-treated microglia display inward rectifying K+ currents partially blocked by Na+.
- A distinct H+ current is present in M-CSF-grown microglia.
- The observed currents share characteristics with those of macrophages, suggesting conserved ion channel functions across myeloid cells.