title: Mechanism of apoptosis induced by diazoxide, a K+ channel opener, in HepG2 human hepatoma cells.
abstract: The effect of diazoxide, a K+ channel opener, on apoptotic cell death was investigated in HepG2 human hepatoblastoma cells. Diazoxide induced apoptosis in a dose-dependent manner and this was evaluated by flow cytometric assays of annexin-V binding and hypodiploid nuclei stained with propidium iodide. Diazoxide did not alter intracellular K+ concentration, and various inhibitors of K+ channels had no influence on the diazoxide-induced apoptosis; this implies that K+ channels activated by diazoxide may be absent in the HepG2 cells. However, diazoxide induced a rapid and sustained increase in intracellular Ca(2+) concentration, and this was completely inhibited by the extracellular Ca(2+) chelation with EGTA, but not by blockers of intracellular Ca(2+) release (dantrolene and TMB-8). This result indicated that the diazoxide-induced increase of intracellular Ca(2+) might be due to the activation of a Ca(2+) influx pathway. Diazoxide-induced Ca(2+) influx was not significantly inhibited by either voltage-operative Ca(2+) channel blockers (nifedipine or verapamil), or by inhibitors of Na+, Ca(2+)-exchanger (bepridil and benzamil), but it was inhibited by flufenamic acid (FA), a Ca(2+)-permeable nonselective cation channel blocker. A quantitative analysis of apoptosis by flow cytometry revealed that a treatment with either FA or BAPTA, an intracellular Ca(2+) chelator, significantly inhibited the diazoxide-induced apoptosis. Taken together, these results suggest that the observed diazoxide-induced apoptosis in the HepG2 cells may result from a Ca(2+) influx through the activation of Ca(2+)-permeable non-selective cation channels. These results are very significant, and they lead us to further suggest that diazoxide may be valuable for the therapeutic intervention of human hepatomas.
authors.affiliation: College of Pharmacy, Duksung Women's University, Seoul 132-714, Korea. yongslee@duksung.ac.kr
authors.forename: Yong Soo
authors.initials: YS
authors.lastname: Lee
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D003981:Diazoxide / Q000494:pharmacology*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology*; D015221:Potassium Channels / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D015221:Potassium Channels; D003981:Diazoxide