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 (I(Cl,Vol)) in glioma cell invasion. Hypotonic solutions ( approximately 230 mOsm) activated outwardly rectifying currents that reversed near the equilibrium potential for Cl(-) ions (E(Cl)). These currents (I(Cl,Vol)) were sensitive to several known Cl(-) channel inhibitors, including DIDS, tamoxifen, and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB). The IC(50) for NPPB inhibition of I(Cl,Vol) was 21 microm. Under isotonic conditions, NPPB (165 microm) 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 microm pores. Inhibition of I(Cl,Vol) with NPPB reduced chemotactic migration in a dose-dependent fashion with an IC(50) of 27 microm. Time-lapse video microscopy during patch-clamp recordings revealed visible changes in cell shape and/or movement that accompanied spontaneous activation of I(Cl,Vol), suggesting that I(Cl,Vol) is activated during cell movement, consistent with the effects of NPPB in migration assays. We propose that I(Cl,Vol) contributes to cell shape and volume changes required for glioma cell migration through brain tissue.

Aquaporin‐1 activity of plasma membrane affects HT20 colon cancer cell migration

“…Previous studies revealed that ion channels and transporters are essential for cell volume regulation and invasive migration of some human tumors (19,20). We proposed that transmembrane water efflux through aquaporin water channels facilitates cell volume change mediated by net salt efflux through ion channels and transporters in the migrating colon cancer cells, leading to enhanced motility and invasion.…”

Chloride/anion channels in glial cell membranes

“…Ransom et al (2001) found that in glioma cells that change shape or that migrate, the I Cl,Vol currents are activated. If these currents are blocked by NPPB or tamoxifen, glioma cell migration is inhibited without affecting survival rate of these cells.…”

“…First described by , a chloride conductance exists in glia-derived tumor cells from humans and animals Ransom et al, 2001). It is not found in normal cells, and the current displayed slight outward rectification, time-and voltage-dependent inactivation, as well as block by tamoxifen.…”

“…If these currents are blocked by NPPB or tamoxifen, glioma cell migration is inhibited without affecting survival rate of these cells. Ransom et al (2001) developed a hypothesis based on these results. Despite their more positive resting potential, glioma cells still have an outward chloride driving force.…”

Glioma Big Potassium Channel Expression in Human Cancers and Possible T Cell Epitopes for Their Immunotherapy

“…Targeting other ion channels, besides gBK channels, could include chloride channel-1 (CLIC1 or its other alias, CLCA1) or aquaporins. Both chloride channel-1 and aquaporins are also overexpressed in glioma (41)(42)(43). BK channel activation leads to cell swelling, whereas CLIC1 activation leads to cell shrinkage (7,8,44).…”