Cb. Ransom et al., Volume-activated, chloride currents contribute to the resting conductance and invasive migration of human glioma cells, J NEUROSC, 21(19), 2001, pp. 7674-7683
We used an in vitro model for glioma cell invasion (transwell migration ass
ay) and patch-clamp techniques to investigate the role of volume-activated
Cl- currents (I-Cl,I-Vol) in glioma cell invasion. Hypotonic solutions (app
roximate to 230 mOsm) activated outwardly rectifying currents that reversed
near the equilibrium potential for Cl- ions (E-Cl). These currents (I-Cl,I
-Vol) were sensitive to several known Cl- channel inhibitors, including DID
S, tamoxifen, and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB). The IC50
for NPPB inhibition of I-Cl,I-Vol was 21 mum. Under isotonic, conditions,
NPPB (165 mum) blocked inward currents (at -40 mV) and increased input resi
stance In both standard whole-cell recordings and amphotericin perforated-p
atch recordings. Reducing [Cl-](circle) under isotonic conditions positivel
y shifted the reversal potential of whole-cell currents. These findings sug
gest a significant resting Cl- conductance in glioma cells. Under isotonic
and hypotonic conditions, Cl- channels displayed voltage- and time-dependen
t inactivation and had an I->Cl- permeability. To assess the potential role
of these channels in cell migration, we studied the chemotactic migration
of glioma cells toward laminin or vitronectin in a Boyden chamber containin
g transwell filters with 8 mum pores. Inhibition of I-Cl,I-Vol with NPPB re
duced chemotactic migration in a dose-dependent fashion with an IC50 of 27
mum. Time-lapse video microscopy during patch-clamp recordings revealed vis
ible changes in cell shape and/or movement that accompanied spontaneous act
ivation of I-Cl,I-Vol, suggesting that I-Cl,I-Vol is activated during cell
movement, consistent with the effects of NPPB in migration assays. We propo
se that I-Cl,I-Vol contributes to cell shape and volume changes required fo
r glioma cell migration through brain tissue.