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Apamin does not inhibit human cardiac Na+current, L-type Ca2+current or other major K+currents

  • Author(s): Yu, CC
  • Ai, T
  • Weiss, JN
  • Chen, PS
  • et al.

Background: Apamin is commonly used as a small-conductance Ca2+-activated K+(SK) current inhibitor. However, the specificity of apamin in cardiac tissues remains unclear. Objective: To test the hypothesis that apamin does not inhibit any major cardiac ion currents. Methods: We studied human embryonic kidney (HEK) 293 cells that expressed human voltage-gated Na+, K+and Ca2+currents and isolated rabbit ventricular myocytes. Whole-cell patch clamp techniques were used to determine ionic current densities before and after apamin administration. Results: Ca2+currents (CACNA1c +CACNB2b) were not affected by apamin (500 nM) (data are presented as median [25thpercentile;75thpercentile] (from -16 [-20;-10] to -17 [-19;-13] pA/pF, P = NS), but were reduced by nifedipine to -1.6 [-3.2;-1.3] pA/pF (p = 0.008). Na+currents (SCN5A) were not affected by apamin (from -261 [-282;-145] to -268 [-379;-132] pA/pF, P = NS), but were reduced by flecainide to -57 [-70;-47] pA/pF (p = 0.018). None of the major K+currents (IKs, IKr, IK1and Ito) were inhibited by 500 nM of apamin (KCNQ1+KCNE1, from 28 [20;37] to 23 [18;32] pA/pF; KCNH2+KCNE2, from 28 [24;30] to 27 [24;29] pA/pF; KCNJ2, from -46 [-48;-40] to -46 [-51;-35] pA/pF; KCND3, from 608 [505;748] to 606 [454;684]). Apamin did not inhibit the INaor ICaLin isolated rabbit ventricular myocytes (INa, from -67 [-75;-59] to -68 [-71;-59] pA/pF; ICaL, from -16 [-17;-14] to -14 [-15;-13] pA/pF, P = NS for both). Conclusions: Apamin does not inhibit human cardiac Na+currents, L-type Ca2+currents or other major K+currents. These findings indicate that apamin is a specific SK current inhibitor in hearts as well as in other organs. © 2014 Yu et al.

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