K+ channels and the microglial respiratory burst

Microglial activation following central nervous system damage or disease of ten culminates in a respiratory burst that is necessary for antimicrobial f unction, but, paradoxically, can damage bystander cells. We show that sever al K+ channels are expressed and play a role in the respiratory burst of cu ltured rat microglia. Three pharmacologically separable K+ currents had pro perties of Kv1.3 and the Ca2+/calmodulin-gated channels, SK2, SK3, and SK4. mRNA was detected for Kv1.3, Kv1.5, SK2, and/or SK3, and SK4. Protein was detected for Kv1.3, Kv1.5, and SK3 (selective SK2 and SK4 antibodies not av ailable). No Kv1.5-like current was detected, and confocal immunofluorescen ce showed the protein to be subcellular, in contrast to the robust membrane localization of Kv1.3. To determine whether any of these channels play a r ole in microglial activation, a respiratory burst was stimulated with phorb ol 12-myristate 13-acetate and measured using a single cell, fluorescence-b ased dihydrorhodamine 123 assay. The respiratory burst was markedly inhibit ed by blockers of SK2 (apamin) and SK4 channels (clotrimazole and charybdot oxin), and to a lesser extent, by the potent Kv1.3 blocker agitoxin-2.