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The Journal of Neurophysiology Vol. 85 No. 2 February 2001, pp. 790-803
Copyright ©2001 by the American Physiological Society
Department of Neurobiology, University of Alabama School of Medicine, Birmingham, Alabama 35294
Ransom, Christopher B. and
Harald Sontheimer.
BK Channels in Human Glioma Cells. J. Neurophysiol. 85: 790-803, 2001. 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, V0.5, 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.
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