Modulation of volume-sensitive Cl^- channels and cell volume by actin filaments and microtubules in human cervical cancer HT-3 cells

Hypotonicity activates volume-sensitive Cl^- currents, which are implicated in the regulatory volume decrease (RVD) responses and transport of taurine in human cervical cancer HT-3 cells. In this study, the role of cytoskeleton in the regulation of volume-sensitive Cl^- channels and RVD responses in HT-3 cells was studied. Cells were incubated with various compounds, which depolymerized or polymerized cytoskeletal elements, i.e. actin filaments and microtubules. The hypotonicity-induced changes in Cl^- conductance and in cell volume were measured by whole-cell voltage clamping and cell size monitoring, respectively. Our results show that in HT-3 cells hypotonicity activated an outward rectified Cl^- current that was abrogated by Cl^- channel blockers. Cytochalasin B, an actin-depolymerizing compound, induced a substantial increase in Cl^- conductance under isotonic condition and potentiated the expression of Cl^- currents in hypotonic stress. Phorbol 12-myristate 13-acetate (PMA) significantly inhibited the cytochalasin B-induced activation of Cl^- conductance under isotonic condition. On the other hand, treatment with cytochalasin B significantly prolonged the RVD responses. Phalloidin, a stabilizer of actin polymerization, did not change the basal currents under isotonic condition, but completely abolished the increase in whole-cell Cl^- conductance elicited by hypotonicity and retarded the cell volume recovery. Colchicine, a microtubule-assembly inhibitor, had no effect on either basal Cl^- conductance or volume-sensitive Cl^- current and was unable to inhibit the RVD responses. Taxol, a microtubule-stabilizing compound, did not alter the basal Cl^- conductance, but inhibited the activation of volume-sensitive Cl^- channels as well as the process of RVD in a dose-dependent manner. These data support the notion that functional integrity of actin filaments and microtubules plays critical roles in maintaining the RVD responses and activation of Cl^- channels in human cervical cancer HT-3 cells.