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.
Choi
Seok
S
Department of Physiology, Research Laboratory for the Study of Ginseng Signal Transduction, College of Veterinary Medicine, Konkuk University, Seoul, South Korea
Lee
Jun Ho
JH
Kim
Yang In
YI
Kang
Man Jong
MJ
Rhim
Hyewon
H
Lee
Sang Mok
SM
Nah
Seung Yeol
SY
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