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

Abstract

Voltage-gated K ϩ (Kv) channels play critical roles in a wide variety of physiological processes, including the regulation of neurotransmitter release, neuronal excitability, heart rate, muscle contraction, hormone secretion, epithelial electrolyte transport, cell volume, and cell proliferation in neuronal and non-neuronal cells.1) Kv channels consist of tetramers of pore-forming Kva and auxiliary Kvb subunits. 1)The Kva subunit is composed of six a-helical transmembrane segments (S1-S6). The S4 segment acts as the voltage-sensing apparatus of the K ϩ channel, 1) while the poreforming S5-S6 segments constitute a selectivity filter and govern voltage-dependent increases in K ϩ permeability. Sitedirected mutagenesis studies using Kva subunits have clarified the detailed action and binding sites of various drugs that regulate Kv channel activity. 1) Some Kv channel a subunits exhibit transient A-type K ϩ currents and N-type inactivation.2) For example, Kv1.4 channels are one of the families of voltage-gated K ϩ channels that mediate rapidly inactivating A-type currents and N-type inactivation. The molecular mechanism of this channel inactivation is thought to be of the N-type; i.e., a "ball" domain within the N-terminal polypeptide structure can occlude the channel from inside, thus blocking current flow. Thus, N-terminal deletions remove inactivation and induce non-inactivating persistent outward K ϩ currents and C-type inactivation. 3-5)Recently, we reported that ginsenoside Rg 3 (20-S-pro-.4 (hKv1.4) channel currents by forming hydrogen bonds between Rg 3 and amino acids, including K531 residue of the channels, using the site-directed mutagenesis method.6) In this report, we present evidence that Rg 3 inhibits preferentially non-inactivating persistent rather than peak outward currents in N-terminal (D2-61) deleted hKv1.4 (hKv1.4D2-61) channels. In addition, mutation of K531 hKv1.4D2-61 to K531Y hKv1.4D2-61 and raising the extracellular [K ϩ ] abolished the inhibitory effect of Rg 3 on non-inactivating plateau outward currents. Rg 3 increases the C-type inactivation rate, but raising the extracellular [K ϩ ] o reverses Rg 3 action on hKv1.4D2-61 channels. These results support that K531 residue also plays an important role in the Rg 3 -mediated noninactivating current blockage of hKv1.4D2-61 channels. KIST; Seoul 130-701, Korea. Received October 22, 2008; accepted January 8, 2009 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 Rg 3 (Rg 3 ), 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) bin...

Relationships between chemical structures and functions of triterpene glycosides isolated from sea cucumbers

“…Furthermore, triterpene glycosides inhibited voltage-gated Na + channels (Na V 1.2 and Na V 1.4) (Lee et al, 2008). In addition, triterpene glycosides could induce K + currents through voltage-gated K + channel (K V 1.4), calcium-activated K + channel (BK Ca ), and human Ether- à -go-go Related Gene (hERG) K + channels (Kv11.1), which might be responsible for their vasodilatory and antiarrhythmic effects (Lee et al, 2009; Choi et al, 2011a,b; Xu and Huang, 2012). The antiepileptic and neuroprotective effects of triterpene glycosides might be due to the inhibition of excitatory N -methyl-D-aspartate (NMDA) receptors and nicotinic acetylcholine receptors, as well as the activation of inhibitory γ-amino butyric acid (GABA) receptors (Lee et al, 2006, 2013a,b).…”

Dependence of 6β-acetoxy-7α-hydroxyroyleanone block of Kv1.2 channels on C-type inactivation

“…Arachidonic acid, a lipid signaling molecule arising from phospholipid metabolism, induces fast inactivation of otherwise non-inactivating Kv channels (Kv1.1 and 3.1) [15] but it also accelerates activation of Kv1.1 [16]. There are other compounds, namely ginsenoside Rg 3 and verapamil, which appear to block Kv channels by accelerating C-type inactivation [22,23]. However, the selectivity of action remains to be confirmed, since their effects on activation gating have not been examined in details.…”

Lipid Membranes as Key Targets for the Pharmacological Actions of Ginsenosides

“…Rg3 can interfere with the activity of ion channels, including human Kv1.4 channel and 5-hydroxytryptamine receptor type 3 (5-HT3A) ( Lee et al., 2004 ). Rg3 inhibits 5-HT3A receptor channel activity by interacting with residues V291, F292, and I295 in the channel-gating region of transmembrane domain 2 ( Lee et al., 2007 ; Lee et al., 2009 ). Moreover, in cultured hippocampal neurons, the activation of glutamate (NMDA) receptors is attenuated by ginsenoside Rh2 and Rg3 via a competitive interaction with its polyamine- or glycine-binding site, respectively ( Kim S. et al., 2004 ; Lee et al., 2006 ).…”