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Pharmacological properties of Ca2+-activated K+ currents of ramified murine brain macrophages
1Abteilung Neurophysiologie, Institut für Physiologie der Charité, Humboldt Universität, Berlin, Germany.
Abstract:
Using the whole-cell configuration of the patch clamp technique, calcium-activated potassium currents (I(K,Ca)) were investigated in ramified murine brain macrophages. In order to induce I(K,Ca) the intracellular concentration of nominal free Ca2+ was adjusted to 1 microM. The Ca2+-activated K+ current of brain macrophages did not show any voltage dependence at test potentials between -120 and +30 mV. A tenfold change in extracellular K+ concentration shifted the reversal potential of I(K,Ca) by 51 mV. The bee venom toxin apamin applied at concentrations of up to 1 microM did not affect I(K,Ca). Ca2+-activated K+ currents of ramified brain macrophages were highly sensitive to extracellularly applied charybdotoxin (CTX). The half-maximal effective concentration of CTX was calculated to be 4.3 nM. In contrast to CTX, the scorpion toxin kaliotoxin did not inhibit I(K,Ca) at concentrations between 1 and 50 nM. Tetraethylammonium (TEA) blocked 8.0% of I(K,Ca) at a concentration of 1 mM, whereas 31.4% of current was blocked by 10 mM TEA. Several inorganic polyvalent cations were tested at a concentration of 2 mM for their ability to block I(K,Ca). La3+ reduced I(K,Ca) by 72.8%, whereas Cd2+ decreased I(K,Ca) by 17.4%; in contrast, Ni2+ did not have any effect on I(K,Ca). Ba2+ applied at a concentration of 1 mM reduced I(K,Ca) voltage-dependently at hyperpolarizing potentials.
Insights
Calcium-activated potassium currents (I(K,Ca)) in brain macrophages are voltage-independent and highly sensitive to charybdotoxin (CTX). These currents are modulated by various cations, offering insights into macrophage ion channel function.
Area of Science:
- Neuroscience
- Cell Biology
- Ion Channel Physiology
Background:
- Ramified murine brain macrophages possess calcium-activated potassium currents (I(K,Ca)).
- Understanding these currents is crucial for elucidating macrophage function in the brain.
Purpose of the Study:
- To characterize the biophysical and pharmacological properties of I(K,Ca) in murine brain macrophages.
- To identify specific modulators of I(K,Ca) in this cell type.
Main Methods:
- Whole-cell patch clamp technique was employed to record I(K,Ca).
- Intracellular free calcium was adjusted to 1 microM to activate the currents.
- Voltage-dependence, ion concentration effects, and blockade by toxins and cations were assessed.
Main Results:
- I(K,Ca) in brain macrophages exhibited no voltage dependence between -120 and +30 mV.
- A tenfold increase in extracellular K+ shifted the reversal potential by 51 mV.
- Charybdotoxin (CTX) potently inhibited I(K,Ca) with an IC50 of 4.3 nM, while apamin and kaliotoxin had no significant effect.
- Tetraethylammonium (TEA) and polyvalent cations like La3+ and Cd2+ showed inhibitory effects, with varying degrees of potency and voltage-dependence.
Conclusions:
- Murine brain macrophage I(K,Ca) are characterized by voltage independence and high sensitivity to CTX.
- These currents are distinct from apamin- and kaliotoxin-sensitive channels.
- The findings provide a detailed profile of I(K,Ca) in brain macrophages, relevant for neuro-inflammatory and immune response research.