Ion channels of human microglia in culture

Macroscopic and microscopic currents have been recorded using human microglia isolated from fetal human brains (12-20 weeks gestation). Within a period of two days following plating of cells, inward K+ currents were small (mean amplitude of 0.3 nA at -100 mV) and outward K+ currents were not observed. For periods in excess of five days after adherence to substrate, an inactivating outward K+ current, sensitive to 4-aminopyridine, was expressed. A slowly rising current, blocked by tetraethylammonium, was also evident in a small population of human microglia. This current was activated with cell depolarization positive to +10 mV and had properties similar to those recently described for a proton current in mouse cells. In early adherent cells (days 1 or 2 after plating), treatment of microglia with interferon-gamma led to the expression of outward K+ current which was lacking in the absence of the treatment. In excised, inside-out patches, two high conductance channels were identified. A calcium-dependent K+ channel (unitary conductance of 106 pS with physiological levels of K+ across the patch) had an open probability of 0.5 with internal Ca2+ at 7 mu M and the patch potential at 0 mV. In addition, an anion channel (unitary conductance of 280 pS) was transiently activated with depolarizing or hyperpolarizing steps applied from 0 mV. Characterization of the macroscopic and unitary properties of currents in microglia will have relevance to a description of putative cell functions in the human CNS. In particular, modification of cell electrophysiological properties by Various activating stimuli may contribute to signalling processes in CNS pathology. (C) 1997 IBRO. Published by Elsevier Science Ltd.