DISTINCT SOLUBLE ASTROCYTIC FACTORS INDUCE EXPRESSION OF OUTWARD K+ CURRENTS AND RAMIFICATION OF BRAIN MACROPHAGES

Isolated cultured murine brain macrophages (BM) were treated with supe rnatants of enriched astrocytic cultures. The astrocyte-conditioned me dium (ACM) induced ramification of BM. In parallel, BM expressed volta ge-gated outward K+ currents (I-K) during the first 2 days after the a pplication of ACM. However, in ramified BM which were treated once wit h ACM, I-K disappeared 5 days after that treatment. In contrast, BM ex pressed 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 di d not inhibit ramification of the cells. Furthermore, after applicatio n of low-concentrated ACM BM exhibited I-K but did not change their mo rphology. It is suggested that in murine BM the ramification and the e xpression of I-K are induced by distinct soluble factors derived from astrocytes. (C) 1997 Elsevier Science Ireland Ltd.