The slowly activating delayed rectifier K(+) channels (I(Ks)) are one of the main pharmacological targets for development of drugs against cardiovascular diseases. Cardiac I(Ks) consists of KCNQ1 plus KCNE1 subunits. Ginsenoside, one of the active ingredient of Panax ginseng, enhances cardiac I(Ks) currents. However, little is known about the molecular mechanisms of how ginsenoside interacts with channel proteins to enhance cardiac I(Ks). In the present study, we investigated ginsenoside Rg(3) (Rg(3)) effects on human I(Ks) by co-expressing human KCNQ1 plus KCNE1 subunits in Xenopus oocytes. Rg(3) enhanced I(Ks) currents in concentration- and voltage-dependent manners. The EC(50) was 15.2+/-8.7 microM. However, in oocytes expressing KCNQ1 alone, Rg(3) inhibited the currents with concentration- and voltage-dependent manners. The IC(50) was 4.8+/-0.6 microM. Since Rg(3) acts opposite ways in oocytes expressing KCNQ1 alone or KCNQ1 plus KCNE1 subunits, we examined Rg(3) effects after co-expression of different ratios of KCNE1 and KCNQ1. The increase of KCNE1/KCNQ1 ratio converted I(Ks) inhibition to I(Ks) activations. One to ten ratio of KCNE1 and KCNQ1 subunit is required for Rg(3) activation of I(Ks). Mutations of K318 and V319 into K318Y and V319Y of KCNQ1 channel abolished Rg(3) effects on KCNQ1 or KCNQ1 plus KCNE1 channel currents. The docked modeling revealed that K318 residue plays a key role in stabilization between Rg(3) and KCNQ1 plus KCNE1 or KCNQ1 subunit. These results indicate that Rg(3)-induced activation of I(Ks) requires co-assembly of KCNQ1 and KCNE1 subunits and achieves this through interaction with residues K318 and V319 of KCNQ1 subunit.
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