Vol. 59, Issue 6, 1376-1387, June 2001

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

Volodymr Rybalchenko, Natalia Prevarskaya, Fabien Van Coppenolle, Guillaume Legrand, Loic Lemonnier, Xuefen Le Bourhis, and Roman Skryma

Laboratoire de Physiologie Cellulaire, Institut National de la Santé et de la Recherche Médicale EPI-9938, USTL, Villeneuve d'Ascq, France

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 (I_K) exhibited neither C-type, nor rapid (human ether á go-go-related gene-type) inactivation. With 2 mM [Mg²⁺]_o, I_K activation kinetics was independent of holding potential, suggesting the absence of ether á go-go-type K⁺ channels. Extracellular applications of TEA and verapamil (IC₅₀ = 11 µM) rapidly (12 s) inhibited I_K 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 I_K, although both phenylalkylamines inhibited single-channel currents in inside-out patches. Extracellular application of N-methyl-verapamil (25 µM) had no influence on I_K. 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 I_K 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.