PROPERTIES OF VOLTAGE-GATED POTASSIUM CURRENTS OF MICROGLIA DIFFERENTIATED WITH GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR

Voltage-gated whole-cell currents were recorded from cultured microgli al cells which had been developed in the presence of the macrophage/mi croglial growth factor granulocyte/macrophage colony-stimulating facto r. Outward K+ currents (I-K) were most prominent in these cells. I-K c ould be activated at potentials more positive than -40 mV. Half-maxima l activation of I-K was achieved at -13.8 mV and half-maximal inactiva tion of I-K was determined at -33.8 mV. The recovery of I-K from inact ivation was described by a time constant of 7.9 sec. For a tenfold cha nge in extracellular K+ concentration the reversal potential of I-K sh ifted by 54 mV. Extracellularly applied 10 mM tetraethylammonium chlor ide reduced I-K by about 50%, while 5 mM 4-aminopyridine almost comple tely abolished I-K. Several divalent cations (Ba2+, Cd2+, Co2+, Zn2+) reduced current amplitudes and shifted the activation curve of I-K to more positive values. Charybdotoxin (IC50 = 1.14 nM) and noxiustoxin ( IC50 = 0.89 nM) blocked I-K in a concentration-dependent manner, where as dendrotoxin and mast cell degranulating peptide had no effect on th e current amplitudes. The outward K+ currents showed a frequency depen dence 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-K was detected. I-K' was blocked completely by 10 mM charybdotoxin or by 10 nM noxiustoxin. In contrast to its eff ect on I-K, 10 mM tetraethylammonium chloride did not reduce I-K'.