Wednesday, 8 December 2010
Ca2+-release activated Ca2+ channel (CRAC)-mediated increase in cytoplasmic Ca2+ concentration (D[Ca2+]c) is a critical early step of signals for the activation of lymphocytes. Also, the voltage-gated K+ channel (Kv) and intermediate-conductance Ca2+-activated K+ channel (IKCa1/SK4) draw attention as pharmacological targets for regulating immune responses. Since polyphenolic agents have various ranges of anti-inflammatory or immunomodulatory effects, here we compared the effects of curcumin, rosmarinic acid, resveratrol and epigallocatechin gallate on the ionic currents through CRAC (ICRAC), Kv (IKv), SK4 (ISK4), and on the D[Ca2+]c in Jurkat-T cells, using fura-2 spectrofluorimetry and patch clamp technique. Curcumin (10 mM) inhibited both anti-CD3 Ab-induced D[Ca2+]c and thapsigargin-induced store-operated Ca2+ entry (SOCE) via CRAC. Ferulic acid and vanillin, the metabolites of curcumin, had no effect on SOCE. Dose-dependent inhibition of ICRAC by curcumin was confirmed in Jurkat T (IC50, 5.9 mM) and the HEK-293 cells overexpressing Orai1 and STIM1 (IC50, 0.6 mM). Also, curcumin potently inhibited both IKv (IC50, 11.9 mM) and ISK4 (IC50, 4.2 mM). The other polyphenols (rosmarinic acid, resveratrol and epigallocatechin gallate at 10 – 30 mM) had no effect on SOCE, and showed only a partial inhibition of the K+ currents. In summary, among the tested polyphenolic agents, curcumin showed prominent inhibition of major ion channels in lymphocytes, which might contribute to the anti-inflammatory effects of curcumin when sufficient concentration is reached in vivo.