Distinct soluble astrocytic factors induce expression of outward K+ currents and ramification of brain macrophages

Isolated cultured murine brain macrophages (BM) were treated with supernatants of enriched astrocytic cultures. The astrocyte-conditioned medium (ACM) induced ramification of BM. In parallel, BM expressed voltage-gated outward K+ currents (I-K) during the first 2 days after the application of ACM. However, in ramified BM which were treated once with ACM, I-K disappeared 5 days after that treatment. In contrast, BM expressed I-K over a period of more than 5 days when cells were treated daily with ACM. A blockade of I-K by charybdotoxin or by kaliotoxin did not inhibit ramification of the cells. Furthermore, after application of low-concentrated ACM BM exhibited I-K but did not change their morphology. It is suggested that in murine BM the ramification and the expression of I-K are induced by distinct soluble factors derived from astrocytes. (C) 1997 Elsevier Science Ireland Ltd.