Properties of voltage-gated potassium currents of microglia differentiated with granulocyte/macrophage colony-stimulating factor

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 (I _K) were most prominent in these cells. I _Kcould be activated at potentials more positive than −40 mV. Half-maximal activation of I _Kwas achieved at −13.8 mV and half-maximal inactivation of I _Kwas determined at −33.8 mV. The recovery of I _Kfrom inactivation was described by a time constant of 7.9 sec. For a tenfold change in extracellular K⁺ concentration the reversal potential of I _Kshifted by 54 mV.

Extracellularly applied 10 mm tetraethylammonium chloride reduced I _K by about 50%, while 5 mm 4-aminopyridine almost completely abolished I _K. Several divalent cations (Ba²⁺, Cd²⁺, Co²⁺, Zn²⁺) reduced current amplitudes and shifted the activation curve of I _Kto more positive values. Charybdotoxin (IC₅₀ = 1.14 nm) and noxiustoxin (IC₅₀=0.89 nm) blocked I _Kin 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 (I _K′) characterized by the same activation behavior as I _Kwas detected. I _K′was blocked completely by 10 nm charybdotoxin or by 10 nm noxiustoxin. In contrast to its effect on I _K, 10 mm tetraethylammonium chloride did not reduce I _K′.