Volume-activated chloride currents contribute to the resting conductance and invasive migration of human glioma cells

Abstract

We used an in vitro model for glioma cell invasion (transwell migration assay) and patch-clamp techniques to investigate the role of volume-activated Cl- currents (ICl,Vol) in glioma cell invasion. Hypotonic solutions (≈230 mOsm) activated outwardly rectifying currents that reversed near the equilibrium potential for Cl- ions (ECl). These currents (ICl,Vol) were sensitive to several known Cl- channel inhibitors, including DIDS, tamoxifen, and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB). The IC50 for NPPB inhibition of ICl,Vol was 21 μM. Under isotonic conditions, NPPB (165 μM) blocked inward currents (at -40 mV) and increased input resistance in both standard whole-cell recordings and amphotericin perforated-patch recordings. Reducing [Cl-]o under isotonic conditions positively shifted the reversal potential of whole-cell currents. These findings suggest a significant resting Cl- conductance in glioma cells. Under isotonic and hypotonic conditions, Cl- channels displayed voltage- and time-dependent 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 containing transwell filters with 8 μm pores. Inhibition of ICl,Vol with NPPB reduced chemotactic migration in a dose-dependent fashion with an IC50 of 27 μM. Time-lapse video microscopy during patch-clamp recordings revealed visible changes in cell shape and/or movement that accompanied spontaneous activation of ICl,Vol, suggesting that ICl,Vol is activated during cell movement, consistent with the effects of NPPB in migration assays. We propose that ICl,Vol contributes to cell shape and volume changes required for glioma cell migration through brain tissue.