Effects of ginsenoside on G protein-coupled inwardly rectifying K+ channel activity expressed in Xenopus oocytes.
Recently, we provided evidence that ginsenoside, the active component of Panax ginseng, uses the pertussis toxin-insensitive Galpha(q/11)-phospholipase C-beta3 signal transduction pathway to increase Ca(2+)-activated Cl(-) currents in the Xenopus oocyte. Other investigators have shown that stimulation of receptors linked to the Galpha(q)-phospholipase C pathway inhibits the activity of G protein-coupled inwardly rectifying K(+) (GIRK) channels. In the present study, we sought to determine whether ginsenoside influenced the activity of GIRK 1 and GIRK 4 (GIRK 1/4) channels expressed in the Xenopus oocyte, and if so, the underlying signal transduction mechanism. In oocytes injected with GIRK 1/4 channel cRNA, bath-applied ginsenoside inhibited the high K(+) solution-elicited GIRK current (EC(50): 4.9+/-4.3 microg/ml). Pretreatment of the oocyte with pertussis toxin reduced the high K(+) solution-elicited GIRK current by 49%, but it did not alter the inhibitory effect of ginsenoside on the GIRK current. Prior intraoocyte injection of cRNA(s) coding Galpha(q), Galpha(11) or Galpha(q)/Galpha(11), but not Galpha(i2) or Galpha(oA), attenuated the inhibitory ginsenoside effect. Injection of cRNAs coding Gbeta(1)gamma(2) also attenuated the ginsenoside effect. Preincubation of GIRK channel-expressing oocytes with phospholipase C inhibitor, [1-[6-((17b-3-Methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione] (U73122), or protein kinase C inhibitor, staurosporine or chelerythrine, blocked the inhibitory ginsenoside effect on the GIRK current. Intraoocyte injection of bis (o-aminophenoxy)ethane-N,N,N',N'-tetracetic acid (BAPTA), a free Ca(2+) chelator, had no significant effect on the action of ginsenoside. Taken together, these results suggest that ginsenoside inhibits the activity of the GIRK 1/4 channel expressed in the Xenopus oocyte through a pertussis toxin-insensitive and Galpha(q/11)-, phospholipase C- and protein kinase C-mediated signal transduction pathway.
Department of Physiology, Research Laboratory for the Study of Ginseng Signal Transduction, College of Veterinary Medicine, Konkuk University, Seoul, South Korea
Seok
S
Choi
Jun Ho
JH
Lee
Yang In
YI
Kim
Man Jong
MJ
Kang
Hyewon
H
Rhim
Sang Mok
SM
Lee
Seung Yeol
SY
Nah
D000818:Animals; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D015870:Gene Expression; D036145:Ginsenosides / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D005894:Panax / Q000737:chemistry*; D037342:Pertussis Toxin / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D018075:RNA, Complementary / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D010738:Type C Phospholipases / Q000378:metabolism; D014982:Xenopus laevis
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D036145:Ginsenosides; D018075:RNA, Complementary; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010738:Type C Phospholipases; D043802:GTP-Binding Protein alpha Subunits, Gq-G11