BK Channels in Human Glioma Cells

Abstract

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 in 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+ ≈ Li+ > Na+. Currents were >80% inhibited by iberiotoxin (33 nM), charybdotoxin (50 nM), quinine (1 mM), tetrandrine (30 μM), and tetraethylammonium ion (TEA; 1 mM). Extracellular phloretin (100 μM), 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 μM [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 fashion proportional to the square-root of [K+]o. Recording from cell-attached patches revealed large conductance channels (150–200 pS) with similar voltage dependence and activation kinetics as whole cell currents. These data indicate that human glioma cells express large-conductance, Ca2+-activated K+ (BK) channels. In amphotericin-perforated patches bradykinin (1 μM) activated TEA-sensitive currents that were abolished by preincubation with bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid-AM (BAPTA-AM). The BK channels described here may influence the responses of glioma cells to stimuli that increase [Ca2+]i.