BK channel openers inhibit migration of human glioma cells

Large-conductance Ca(2+)-activated K(+) channels (BK channels) are highly expressed in human glioma cells. However, less is known about their biological function in these cells. We used the patch-clamp technique to investigate activation properties of BK channels and time-lapse microscopy to evaluate the role of BK channel activation in migration of 1321N1 human glioma cells. In whole cells, internal perfusion with a solution containing 500 nM free Ca(2+) and external application of the BK channel opener phloretin (100 micro M) shifted the activation threshold of BK channel currents toward more negative voltages of about -30 mV, which is close to the resting potential of the cells. The concentration of intracellular Ca(2+) in fura-2-loaded 1321N1 cells was measured to be 235+/-19 nM and was increased to 472+/-25 nM after treatment with phloretin. Phloretin and another BK channel opener NS1619 (100 micro M) reduced the migration velocity by about 50%. A similar reduction was observed following muscarinic stimulation of glioma cells with acetylcholine (100 micro M). The effects of phloretin, NS1619 and acetylcholine on cell migration were completely abolished by co-application of the specific BK channel blockers paxilline (5 micro M) and iberiotoxin (100 nM). The phloretin-induced increase in intracellular Ca(2+) was unaffected by the removal of extracellular Ca(2+) and co-application of paxilline. These findings indicate that glioma cell migration was inhibited through BK channel activation, independent of intracellular Ca(2+).