BK channels in human glioma cells

Ion channels in inexcitable cells are involved in proliferation and volume regulation. Glioma cells robustly proliferate and undergo shape and volume changes during invasive migration. We investigated ion channel expression i n two human glioma cell lines (D54MG and STTG-1). With low [Ca2+](i), both cell types displayed voltage-dependent currents that activated at positive voltages (more than +50 mV). Current density was sensitive to intracellular cation replacement with the following rank order; K+ > Cs+ approximate to Li+ > Na+. Currents were >80% inhibited by iberiotoxin (33 nM), charybdotox in (50 nM), quinine (1 mM), tetrandrine (30 muM), and tetraethylammonium io n (TEA; 1 mM). Extracellular phloretin (100 muM), an activator of BK(Ca2+) channels, and elevated intracellular Ca2+ negatively shifted the I-V curve of whole cell currents. With 0, 0.1, and 1 muM [Ca2+](i), the half-maximal voltages, V-0.5, for whole cell current activation were +150, +65, and +12 mV, respectively. Elevating [K+](o) potentiated whole cell currents in a fa shion proportional to the square-root of [K+](o). Recording from cell-attac hed patches revealed large conductance channels (150-200 pS) with similar v oltage dependence and activation kinetics as whole cell currents. These dat a indicate that human glioma cells express large-conductance, Ca2+-activate d K+ (BK) channels. In amphotericin-perforated patches bradykinin (1 muM) a ctivated TEA-sensitive currents that were abolished by preincubation with b is-(oaminophenoxy)-N,N,N',N'- tetraacetic acid-AM (BAPTA-AM). The BK channe ls described here may influence the responses of glioma cells to stimuli th at increase [Ca2+](i).