Recently we demonstrated that ginsenosides, the active ingredients of Panax ginseng, enhanced Ca2+-activated Cl- current in the Xenopus oocyte through a signal transduction mechanism involving the activation of pertussis toxin-insensitive G protein and phospholipase C (PLC). However, it has not yet been determined precisely which G protein subunit(s) and which PLC isoform(s) participate in the ginsenoside signaling. To provide answers to these questions, we investigated the changes in ginsenoside effect on the Cl- current after intraoocyte injections of the cRNAs coding various G protein subunits, a regulator of G protein signaling (RGS2), and Gβγ-binding proteins. In addition, we examined which of mammalian PLCβ1-3 antibodies injected into the oocyte inhibited the action of ginsenosides on the Cl- current. Injection of Gαq or Gα11 cRNA increased the basal Cl- current recorded 48 h after, and it further prevented ginsenosides from enhancing the Cl- current, whereas Gα12 and GαoA cRNA injection had no significant effect. The changes following Gα q cRNA injection were prevented when Gβ1γ 2 and Gαq subunits were co-expressed by simultaneous injection of the cRNAs coding these subunits. Injection of cRNA coding GαqQ209L, a constitutively active mutant that does not bind to Gβγ, produced effects similar to those of Gα q cRNA injection. The effects of GαqQ209L cRNA injection, however, were not prevented by co-injection of Gβ 1γ2 cRNA. Injection of the cRNA coding RGS2, which interacts most selectively with Gαq/11 among various identified RGS isoforms and stimulates the hydrolysis of GTP to GDP in active GTP-bound Gα subunit, resulted in a severe attenuation of ginsenoside effect on the Cl- current. Finally, antibodies against PLCβ3, but not -β1 and -β2, markedly attenuated the ginsenoside effect examined at 3-h postinjection. These results suggest that Gα q/11 coupled to mammalian PLC β3-like enzyme mediates ginsenoside effect on Ca2+-activated Cl- current in the Xenopus oocyte.
ASJC Scopus subject areas