The Blocking Activity of Different Toxins against Potassium Channels Kv3.4 in RLE Cells

Background: K+ channel toxins are essential tools for the first purifications, analysis of subunit structures and brain localization of voltage-gated K+ (Kv) channels. The effects of a lot of toxins on Kv are not fully known. Methods: Using whole-cell patch clamping technique the action of a series of toxins on Kv3.4 current in rat liver cells with expressed Kv3.4 channels (RLE) cloned cells was investigated. The cells were grown in Williams E medium and after 6-8 days, they were suitable for patch clamping. A family of currents was recorded during voltage-clamp steps to various potentials applied from a holding potential of -60 mV to 60-80 mV in 10 mV increments. Results: Upon depolarization, all channels were opened with a sigmoidal time course, reached to the peak within a few 10th of milliseconds and then slowly inactivated. Bath application of tetraethyl ammonium (TEA) or 3, 4-diaminopyridine (DAP) reduced the current dose dependently and inhibited it completely at 3 mM and 25 muM respectively. The Bunodosoma granulifera (BgK) and Heteractis magnifica (HmK) toxins at concentrations up to 30 and 10 muM respectively could not completely inhibit the current. On the hand, toxins such as beta-bungarotoxin, corotoxin, novel toxin and dendrotoxins I (DIP) and K (DPK) even in high concentrations (up to 100 mM) had not any significant effect on Kv3.4 current. Comparison of chemical structures of these effective agents with other reported effective toxins such as blood depressing substances (BDS I and II) show no homology between them, but specially the potency of 3, 4-DAP is comparable with these toxins. Conclusion: These results showed that, the Kv3.4 is more sensitive than other Kv3.4 channels.