Characteristics of ginsenoside Rg3-mediated brain Na+ current inhibition.
We demonstrated previously that ginsenoside Rg(3) (Rg(3)), an active ingredient of Panax ginseng, inhibits brain-type Na(+) channel activity. In this study, we sought to elucidate the molecular mechanisms underlying Rg(3)-induced Na(+) channel inhibition. We used the two-microelectrode voltage-clamp technique to investigate the effect of Rg(3) on Na(+) currents (I(Na)) in Xenopus laevis oocytes expressing wild-type rat brain Na(V)1.2 alpha and beta1 subunits, or mutants in the channel entrance, the pore region, the lidocaine/tetrodotoxin (TTX) binding sites, the S4 voltage sensor segments of domains I to IV, and the Ile-Phe-Met inactivation cluster. In oocytes expressing wild-type Na(+) channels, Rg(3) induced tonic and use-dependent inhibitions of peak I(Na). The Rg(3)-induced tonic inhibition of I(Na) was voltage-dependent, dose-dependent, and reversible, with an IC(50) value of 32 +/- 6 microM. Rg(3) treatment produced a 11.2 +/- 3.5 mV depolarizing shift in the activation voltage but did not alter the steady-state inactivation voltage. Mutations in the channel entrance, pore region, lidocaine/TTX binding sites, or voltage sensor segments did not affect Rg(3)-induced tonic blockade of peak I(Na). However, Rg(3) treatment inhibited the peak and plateau I(Na) in the IFMQ3 mutant, indicating that Rg(3) inhibits both the resting and open states of Na(+) channel. Neutralization of the positive charge at position 859 of voltage sensor segment domain II abolished the Rg(3)-induced activation voltage shift and use-dependent inhibition. These results reveal that Rg(3) is a novel Na(+) channel inhibitor capable of acting on the resting and open states of Na(+) channel via interactions with the S4 voltage-sensor segment of domain II.
Lee
Jun-Ho
JH
Research Laboratory for the Study of Ginseng Signal Transduction, Dept. of Physiology, College of Veterinary Medicine, Konkuk University, Seoul, Korea.
Jeong
Sang Min
SM
Kim
Jong-Hoon
JH
Lee
Byung-Hwan
BH
Yoon
In-Soo
IS
Lee
Joon-Hee
JH
Choi
Sun-Hye
SH
Kim
Dong-Hyun
DH
Rhim
Hyewhon
H
Kim
Sung Soo
SS
Kim
Jai-Il
JI
Jang
Choon-Gon
CG
Song
Jin-Ho
JH
Nah
Seung-Yeol
SY
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D018076:DNA, Complementary; D036145:Ginsenosides / Q000494:pharmacology*; D008012:Lidocaine / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D051381:Rats; D015222:Sodium Channels / Q000235:genetics; D014982:Xenopus laevis
D018076:DNA, Complementary; D036145:Ginsenosides; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; C568253:Scn2A protein, rat; D015222:Sodium Channels; C097367:ginsenoside Rg3; D008012:Lidocaine