Functional expression of a novel ginsenoside Rf binding protein from rat brain mRNA in Xenopus laevis oocytes.
We have shown that ginsenoside Rf (Rf) regulates voltage-dependent Ca(2+) channels through pertussis toxin (PTX)-sensitive G proteins in rat sensory neurons. These results suggest that Rf can act through a novel G protein-linked receptor in the nervous system. In the present study, we further examined the effect of Rf on G protein-coupled inwardly rectifying K(+) (GIRK) channels after coexpression with size-fractionated rat brain mRNA and GIRK1 and GIRK4 (GIRK1/4) channel cRNAs in Xenopus laevis oocytes using two-electrode voltage-clamp techniques. We found that Rf activated GIRK channel in a dose-dependent and reversible manner after coexpression with subfractions of rat brain mRNA and GIRK1/4 channel cRNAs. This Rf-evoked current was blocked by Ba(2+), a potassium channel blocker. The size of rat brain mRNA responding to Rf was about 6 to 7 kilobases. However, Rf did not evoke GIRK current after injection with this subfraction of rat brain mRNA or GIRK1/4 channel cRNAs alone. Other ginsenosides, such as Rb(1) and Rg(1), evoked only slight induction of GIRK currents after coexpression with the subfraction of rat brain mRNA and GIRK1/4 channel cRNAs. Acetylcholine and serotonin almost did not induce GIRK currents after coexpression with the subfraction of rat brain mRNA and GIRK1/4 channel cRNAs. Rf-evoked GIRK currents were not altered by PTX pretreatment but were suppressed by intracellularly injected guanosine-5'-(2-O-thio) diphosphate, a nonhydrolyzable GDP analog. These results indicate that Rf activates GIRK channel through an unidentified G protein-coupled receptor in rat brain and that this receptor can be cloned by the expression method demonstrated here.
Choi
Seok
S
National Research Laboratory for the Study of Ginseng Signal Transduction and Department of Physiology, College of Veterinary Medicine, Chonnam National University, Kwangju, Korea.
Jung
Se-Yeon
SY
Ko
Yoo-Seung
YS
Koh
Seong-Ryong
SR
Rhim
Hyewhon
H
Nah
Seung-Yeol
SY
D000818:Animals; D001921:Brain / Q000378:metabolism / Q000502:physiology*; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D036145:Ginsenosides; D009865:Oocytes; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012503:Saponins / Q000378:metabolism / Q000494:pharmacology*; D014162:Transfection; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D036145:Ginsenosides; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D012503:Saponins; C055328:ginsenoside Rf