Ion channel expression in resting and activated microglia of hippocampal slices from juvenile mice.

Ion channels have frequently been studied in isolated cultured microglia, whereas only little is known about the physiological properties of microglia in situ. In this study, expression of voltage-gated and Ca(2+)-activated ion channels was investigated in microglial cells of acutely prepared and briefly cultured hippocampal slices from juvenile mice. In contrast to microglia of adult brain slices, microglia of slices from juvenile mice exhibited a complex ion channel pattern. Resting microglial cells of acute slices expressed inward rectifier and outward rectifier K(+) channels as well as Zn(2+)-sensitive voltage-activated H(+) channels. In activated microglia of briefly cultured slices, expression levels of both K(+) channel types were upregulated, while H(+) channel expression remained unchanged. In addition, microglia of cultured slices exhibited Ca(2+)-activated K(+) currents, which were not seen in microglia of acute slices, and differed from those expressed in isolated cultured murine microglia. In situ, microglial Ca(2+)-activated K(+) channels were voltage- and Ca(2+)-dependent, had a large single-channel conductance and were inhibited by tetraethylammonium. In summary, our data indicate that the physiological properties of microglia in acute and cultured hippocampal slices from juvenile mice differ markedly from those of microglia cultured in vitro and from those of microglia in adult brain slices.