Verapamil Inhibits Proliferation of LNCaP Human Prostate Cancer Cells Influencing K+ Channel Gating

  1. Volodymr Rybalchenko,
  2. Natalia Prevarskaya,
  3. Fabien Van Coppenolle,
  4. Guillaume Legrand,
  5. Loic Lemonnier,
  6. Xuefen Le Bourhis and
  7. Roman Skryma
  1. Laboratoire de Physiologie Cellulaire, Institut National de la Santé et de la Recherche Médicale EPI-9938, USTL, Villeneuve d'Ascq, France

    Abstract

    The mechanisms of verapamil and tetraethylammonium (TEA) inhibition of voltage-gated K+ channels in LNCaP human prostate cancer cells were studied in whole-cell and outside/inside-out patch-clamp configurations. Rapidly activating outward K+currents (IK) exhibited neither C-type, nor rapid (human ether á go-go-related gene–type) inactivation. With 2 mM [Mg2+]o, IK activation kinetics was independent of holding potential, suggesting the absence of etherá go-go-type K+ channels. Extracellular applications of TEA and verapamil (IC50 = 11 μM) rapidly (12 s) inhibited IK in LNCaP cells. Blocking was also rapidly reversible. Intracellular TEA (1 mM), verapamil (1 mM), and membrane-impermeable N-methyl-verapamil (25 μM) did not influence whole-cell IK, although both phenylalkylamines inhibited single-channel currents in inside-out patches. Extracellular application of N-methyl-verapamil (25 μM) had no influence on IK. Our results are compatible with the hypothesis that, in LNCaP cells expressing C-type inactivation-deficient voltage-activated K+ channels, phenylalkylamines interact with an intracellular binding site, and probably an additional hydrophobic binding site that does not bind charged phenylalkylamines. The inhibiting effects of verapamil and TEA on IK were additive, suggesting independent K+-channel blocking mechanisms. Indeed, TEA (1 mM) reduced a single-channel conductance (from 7.3 ± 0.5 to 3.2 ± 0.4 pA at a membrane potential of +50 mV, n = 6), whereas verapamil (10 μM) reduced an open-channel probability (from 0.45 ± 0.1 in control to 0.1 ± 0.09 in verapamil-treated cells, n = 9). The inhibiting effects of verapamil and TEA on LNCaP cell proliferation were not multiplicative, suggesting that both share a common antiproliferative mechanism initiated through a K+ channel block.

    Footnotes

    • Send reprint requests to: Professor Roman Skryma, Laboratoire de Physiologie Cellulaire, INSERM EPI-9938, USTL, Bat. SN3, 59655 Villeneuve d'Ascq Cedex, France. E-mail:roman.skryma{at}pop.univ-lille1.fr

    • This work was supported by grants from INSERM, Ministère de l'Education Nationale, Association pour la Recherche Contre le Cancer, Ligue Nationale Contre le Cancer, Association pour le Recherche sur les Tumeurs de la Prostate, and Institut de Recherche Pierre Fabre, France.

    • Abbreviations:
      HERG
      human ether à go-go related gene
      TEA
      tetraethylammonium
      Ivrp
      resting K+current in the presence of verapamil
      Icontrol
      control K+ current
      EAG
      ether à go-go
      IK
      K+ current
      IC50
      half-maximal inhibition concentration
      γ
      index of interaction between two inhibitors
      ITEA
      potassium current amplitude inhibited by tetraethylammonium
      I-V, current-voltage
      Itea
      resting K+ current in the presence of tetraethylammonium
      Po
      open probability
      i/Imax
      normalized resting ion current
      • Received July 31, 2000.
      • Accepted February 9, 2001.
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    1. Molecular Pharmacology June 1, 2001 vol. 59 no. 6 1376-1387
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