Large conductance Ca2+-activated K+ channels in human meningioma cells

Cells from ten human meningiomas were electrophysiologically characterized in both living tissue slices and primary cultures. In whole cells, depolarization to voltages higher than +80 mV evoked a large Kt outward current, which could be blocked by iberiotoxin (100 nh3) and TEA (half blocking concentration 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 both sides of the patch). V-1/2 of single-channel currents was +6, -12, -46, and -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 probability (P-o) of BKCa channels was nearly zero at potentials below +80 mV, matching the activation threshold for whole-cell K+ currents with 10 nM Ca2+ in the pipette. Application of 20 mu M cytochalasin D increased P-o of BKVCa channels in cell-attached patches within minutes. These data suggest that the activation of BKCa channels in meningioma cells does not only depend on voltage and internal Ca2+ but is also controlled by the cytoskeleton.