title: Evidence for the Inhibition by Temozolomide, an Imidazotetrazine Family Alkylator, of Intermediate-Conductance Ca2+-Activated K+ Channels in Glioma Cells.
abstract: BACKGROUND
  Temozolomide (TMZ), an oral alkylator of the imidazotetrazine family, is used to treat glioma. Whether this drug has any ionic effects in glioma cells remains largely unclear.
  
  
  METHODS
  With the aid of patch-clamp technology, we investigated the effects of TMZ on the ionic currents in U373 glioma cells. The mRNA expression of KCNN4 (KCa3.1) in U373 glioma cells and TMZ's effect on K+ currents in these KCNN4 siRNA-transfected U373 cells were investigated.
  
  
  RESULTS
  In whole-cell recordings, TMZ decreased the amplitude of voltage-dependent K+ currents (IK) in U373 cells. TMZ-induced IK inhibition was reversed by ionomycin or 1-ethyl-2-benzimidazolinone (1-EBIO). In cell-attached configuration, TMZ concentration-dependently reduced the activity of intermediate-conductance Ca2+-activated K+ (IKCa) channels with an IC50 value of 9.2 µM. Chlorzoxazone or 1-EBIO counteracted the TMZ-induced inhibition of IKCa channels. Although TMZ was unable to modify single-channel conductance, its inhibition of IKCa channels was weakly voltage-dependent and accompanied by a significant prolongation in the slow component of mean closed time. However, neitherlarge-conductance Ca2+-activated (BKCa) nor inwardly rectifying K+ (Kir) channels were affected by TMZ. In current-clamp mode, TMZ depolarized the cell membrane and 1-EBIO reversed TMZ-induced depolarization. TMZ had no effect on IK in KCNN4 siRNA-transfected U373 cells.
  
  
  CONCLUSIONS
  In addition to the DNA damage it does, its inhibitory effect on IKCa channels accompanied by membrane depolarization could be an important mechanism underlying TMZ-induced antineoplastic actions.
authors.forename: Poh-Shiow
authors.initials: PS
authors.lastname: Yeh
authors.forename: Shyh-Jong
authors.initials: SJ
authors.lastname: Wu
authors.forename: Te-Yu
authors.initials: TY
authors.lastname: Hung
authors.forename: Yan-Ming
authors.initials: YM
authors.lastname: Huang
authors.forename: Chia-Wei
authors.initials: CW
authors.lastname: Hsu
authors.forename: Chun-I
authors.initials: CI
authors.lastname: Sze
authors.forename: Yi-Jung
authors.initials: YJ
authors.lastname: Hsieh
authors.forename: Chin-Wei
authors.initials: CW
authors.lastname: Huang
authors.forename: Sheng-Nan
authors.initials: SN
authors.lastname: Wu
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity*; D001562:Benzimidazoles / Q000494:pharmacology; D045744:Cell Line, Tumor; D004249:DNA Damage / Q000187:drug effects*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000633:toxicity; D005910:Glioma; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077204:Temozolomide
chemical_list: D000477:Alkylating Agents; D001562:Benzimidazoles; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496923:KCNN4 protein, human; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D034741:RNA, Small Interfering; D015759:Ionomycin; D003606:Dacarbazine; C102635:1-ethyl-2-benzimidazolinone; D000077204:Temozolomide