BK channel openers inhibit migration of human glioma cells

Abstract

Large-conductance Ca²⁺-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 Ca²⁺ and external application of the BK channel opener phloretin (100 µM) 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 Ca²⁺ 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 µM) reduced the migration velocity by about 50%. A similar reduction was observed following muscarinic stimulation of glioma cells with acetylcholine (100 µM). The effects of phloretin, NS1619 and acetylcholine on cell migration were completely abolished by co-application of the specific BK channel blockers paxilline (5 µM) and iberiotoxin (100 nM). The phloretin-induced increase in intracellular Ca²⁺ was unaffected by the removal of extracellular Ca²⁺ and co-application of paxilline. These findings indicate that glioma cell migration was inhibited through BK channel activation, independent of intracellular Ca²⁺.