The Effects of Ginsenoside Rg₃ on Human Kv1.4 Channel Currents without the N-Terminal Rapid Inactivation Domain

Abstract

Kv1.4 channel belongs to the family of voltage-gated potassium channels that mediate transient and rapidly inactivating A-type currents and N-type inactivation. This N-type inactivation can be removed by the deletion of N-terminal domains, which exhibit non-inactivating currents and C-type inactivation. In our previous report, we demonstrated that 20(S)-ginsenoside Rg₃ (Rg₃), one of the active ingredients of ginseng saponins, inhibits human Kv1.4 (hKv1.4) channel currents through the interaction with amino acids, including Lys (K) residue, which is known as K⁺ activation and the extracellular tetraethylammonium (TEA) binding site. In the present study, we examined the effects of Rg₃ on hKv1.4 channel currents without the N-terminal rapid inactivation domain. We constructed hKv1.4Δ2-61 channels by N-terminal deletion of 2-61 amino acid residues. We investigated the effect of Rg₃ on hKv1.4Δ2-61 channel currents. We found that Rg₃ preferentially inhibited non-inactivating outward currents rather than peak outward currents of hKv1.4Δ2-61 channels. The mutation of K531 hKv1.4Δ2-61 to K531Y hKv1.4Δ2-61 and raising of extracellular [K⁺]_o abolished Rg₃ inhibitions on non-inactivating outward currents. Rg₃ treatment increased the C-type inactivation rate, but raising the extracellular [K⁺]_o reversed Rg₃ action. These results provide additional evidence that K531 residue also plays an important role in the Rg₃-mediated non-inactivating current blockages and in Rg₃-mediated increase of the C-type inactivation rate in hKv1.4Δ2-61 channels.