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 cytoskeleto n in the regulation of volume-sensitive Cl- channels and RVD responses in H T-3 cells was studied. Cells were incubated with various compounds, which d epolymerized or polymerized cytoskeletal elements, i.e. actin filaments and microtubules. The hypotonicity-induced changes in Cl- conductance and in c ell volume were measured by whole-cell voltage clamping and cell size monit oring, respectively. Our results show that in HT-3 cells hypotonicity activ ated an outward rectified Cl- current that was abrogated by Cl- channel blo ckers. Cytochalasin B, an actin-depolymerizing compound, induced a substant ial increase in Cl- conductance under isotonic condition and potentiated th e expression of Cl- currents in hypotonic stress. Phorbol 12-myristate 13-a cetate (PMA) significantly inhibited the cytochalasin B-induced activation of Cl- conductance under isotonic condition. On the other hand, treatment w ith cytochalasin B significantly prolonged the RVD responses. Phalloidin, a stabilizer of actin polymerization, did not change the basal currents unde r isotonic condition, but completely abolished the increase in whole-cell C l- conductance elicited by hypotonicity and retarded the cell volume recove ry. Colchicine, a microtubule-assembly inhibitor, had no effect on either b asal Cl- conductance or volume-sensitive Cl- current and was unable to inhi bit the RVD responses. Taxol, a microtubule-stabilizing compound, did not a lter the basal Cl- conductance, but inhibited the activation of volume-sens itive Cl- channels as well as the process of RVD in a dose-dependent manner . These data support the notion that functional integrity of actin filament s and microtubules plays critical roles in maintaining the RVD responses an d activation of Cl- channels in human cervical cancer HT-3 cells.