Cells from ten human meningiomas were electrophysiologically characterized
in both living tissue slices and primary cultures. In whole cells, depolari
zation to voltages higher than +80 mV evoked a large Kt outward current, wh
ich could be blocked by iberiotoxin (100 nh3) and TEA (half blocking concen
tration IC50 5.3 mM). Raising the internal Ca2+ from 10 nM to 2 mM shifted
the voltage of half-maximum activation (V-1/2) of the K+ current from +106
to +4 mV. Respective inside-out patch recordings showed a voltage- and Ca2 activated (BKCa) K+ channel with a conductance of 296 pS (130 mM K+ at bot
h sides of the patch). V-1/2 of single-channel currents was +6, -12, -46, a
nd -68 mV in the presence of 1, 10, 100, and 1000 mu M Ca2+, respectively,
at the internal face of the patch. In cell-attached patches the open probab
ility (P-o) of BKCa channels was nearly zero at potentials below +80 mV, ma
tching the activation threshold for whole-cell K+ currents with 10 nM Ca2in the pipette. Application of 20 mu M cytochalasin D increased P-o of BKVC
a channels in cell-attached patches within minutes. These data suggest that
the activation of BKCa channels in meningioma cells does not only depend o
n voltage and internal Ca2+ but is also controlled by the cytoskeleton.