Blockade of voltage-gated outward K + currents of ramified murine microglia by scorpion peptide toxins

Microglial cells were cultured from murine neonatal brain. Ramification of isolated microglia could be induced by the application of astrocyte-conditioned medium (ACM). Voltage-gated outward potassium currents ( I K) were measured in ramified microglial cells 12–24 h after their treatment with ACM. The effects of the specific K + channel blockers charybdotoxin (CTX), noxiustoxin (NTX) and kaliotoxin (KTX) on I K of ramified microglia were studied. All these peptide toxins blocked I K in a concentration-dependent manner, while showing a high sensitivity for I K. A half-maximal effective concentration (IC 50) of CTX was estimated to be 1.13 nM, while IC 50 values of 1.24 nM and of 0.81 nM were calculated for KTX and for NTX, respectively. In contrast, dendrotoxin (DTX) did not show any effect on I K. It is suggested that ramified microglial cells express outward K + currents exhibiting pharmacological properties similar that of outward K + currents in cytokine-activated ameboid microglia.