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The Journal of Neuroscience, July 2, 2003, 23(13):5572-5582
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Expression of Voltage-Gated Chloride Channels in Human Glioma Cells
M. L. Olsen,
S. Schade,
S. A. Lyons,
M. D. Amaral, and
H. Sontheimer
Department of Neurobiology and Civitan International Research Center,
University of Alabama at Birmingham, Birmingham, Alabama 35294
Voltage-gated chloride channels have recently been implicated as being
important for cell proliferation and invasive cell migration of primary brain
tumors cells. In the present study we provide several lines of evidence that
glioma Cl currents are primarily mediated by ClC-2 and
ClC-3, two genes that belong to the ClC superfamily. Transcripts for ClC-2
thru ClC-7 were detected in a human glioma cell line by PCR, whereas only
ClC-2, ClC-3, and ClC-5 protein could be identified by Western blot. Prominent
ClC-2, -3, and -5 channel expression was also detected in acute patient
biopsies from low- and high-grade malignant gliomas. Immunogold electron
microscopic studies as well as digital confocal imaging localized a portion of
these ClC channels to the plasma membrane. Whole-cell patch-clamp recordings
show the presence of two pharmacologically and biophysically distinct
Cl currents that could be specifically reduced by 48 hr
exposure of cells to channel-specific antisense oligonucleotides. ClC-3
antisense selectively and significantly reduced the expression of outwardly
rectifying current with pronounced voltage-dependent inactivation. Such
currents were sensitive to DIDS (200500 µM) and
5-nitro-2-(3-phenylpropylamino) benzoic acid (165 µM). ClC-2
antisense significantly reduced expression of inwardly rectifying currents,
which were potentiated by hyperpolarizing prepulses and inhibited by
Cd2+ (200500 µm). Currents that were mediated by ClC-5
could not be demonstrated. We suggest that ClC-2 and ClC-3 channels are
specifically upregulated in glioma membranes and endow glioma cells with an
enhanced ability to transport Cl. This may in turn
facilitate rapid changes in cell size and shape as cells divide or invade
through tortuous extracellular brain spaces.
Key words: ClC channel; brain tumor; patch clamp; antisense knockdown; cell migration; cell proliferation
Received Dec. 12, 2002;
revised Apr. 23, 2003;
accepted Apr. 23, 2003.
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