TRPM4 Channels Mediate Hypertonicity-induced, Ca²⁺-impermeable, Non-selective Cation Currents in a Cervical Cancer Cell Line, HeLa Cells

  • GOMI Simmon
    Department of Molecular Pharmacology, Shinshu University School of Medicine Department of Cardiovascular Medicine, Shinshu University School of Medicine
  • NAKADA Tsutomu
    Department of Molecular Pharmacology, Shinshu University School of Medicine
  • KASHIHARA Toshihide
    Department of Molecular Pharmacology, Shinshu University School of Medicine
  • IKEDA Uichi
    Department of Cardiovascular Medicine, Shinshu University School of Medicine
  • YAMADA Mitsuhiko
    Department of Molecular Pharmacology, Shinshu University School of Medicine

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  • TRPM4 Channels Mediate Hypertonicity-induced, Ca<sup>2+</sup>-impermeable, Non-selective Cation Currents in a Cervical Cancer Cell Line, HeLa Cells

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When extracellular osmolarity exceeds intracellular osmolarity, cells initially shrink but then approach the original cell volume by so-called regulatory cell volume increase (RVI). RVI operates under physiological conditions so that impairment of RVI leads to immediate cell cycle arrest and apoptosis. In a cervical cancer cell line, HeLa cells, extracellular hypertonicity induced non-selective cation currents (IHO currents) which transported mainly Na+ into cells to induce RVI as assessed with the patch-clamp method. Ion channels mediating these currents were Ca2+-impermeable and sensitive to flufenamic acid (FFA) and econazole but not to amiloride or ruthenium red. RT-PCR indicated that HeLa cells express transient receptor potential (TRP) C1, C6, M3, M4, M7, M8, V1 and V2 subunits which form non-selective cation channels. From these results, we speculated that TRPM4 may mediate IHO currents. Indeed, transduction of a dominant-negative TRPM4 subunit significantly inhibited IHO currents. TRPM4 channels became insensitive to hypertonic stimulus when intracellular Ca2+ was strongly buffered. Thus, extracellular hypertonicity activates TRPM4 channels through intracellular Ca2+ to induce RVI in HeLa cells. These results indicate that intra-uterus or -vaginal application of drugs blocking TRPM4 channels may cause antiproliferative/proapoptotic effects on cervical cancer.

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