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 K(+) outward current, which could be blocked by iberiotoxin (100 nm) and TEA (half blocking concentration IC(50) = 5.3 mm). Raising the internal Ca(2+) 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 Ca(2+)-activated (BK(Ca)) 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 microm Ca(2+), respectively, at the internal face of the patch. In cell-attached patches the open probability (P(o)) of BK(Ca) channels was nearly zero at potentials below +80 mV, matching the activation threshold for whole-cell K(+) currents with 10 nm Ca(2+) in the pipette. Application of 20 microm cytochalasin D increased P(o) of BK(Ca) channels in cell-attached patches within minutes. These data suggest that the activation of BK(Ca) channels in meningioma cells does not only depend on voltage and internal Ca(2+) but is also controlled by the cytoskeleton.