Inflammatory stimuli induce a new K+ outward current in cultured rat microglia.

Membrane currents of cultured rat microglia were recorded with the whole-cell patch clamp technique. Undifferentiated microglia express only inwardly rectifying K+ channels. However, treatment of the cells with bacterial lipopolysaccharide, interferon-gamma, or their incubation in hydrophobic teflon bags, procedures that promote microglial differentiation, induced the expression of an additional outward current. Cycloheximide prevented the development of this conductance indicating the synthesis of a new channel protein. The reversal potential of the outward current was near to the K+ equilibrium potential; the current was abolished by intracellular Cs+ or extracellular 4-aminopyridine, and was depressed by extracellular tetraethylammonium. Hence, the channels involved appear to be highly selective for K+; their possible function is a rapid termination of depolarizing shifts of the membrane potential.