A novel activation of Ca(2+)-activated Cl(-) channel in Xenopus oocytes by Ginseng saponins: evidence for the involvement of phospholipase C and intracellular Ca(2+) mobilization.
1. The signal transduction mechanism of ginsenosides, the active ingredients of ginseng, was studied in Xenopus oocytes using two-electrode voltage-clamp technique. Ginseng total saponin (GTS), i.e., an unfractionated mixture of ginsenosides produced a large outward current at membrane potentials more positive than -20 mV when it was applied to the exterior of oocytes, but not when injected intracellularly. The effect of GTS was concentration-dependent (EC(50): 4.4 microg ml(-1)) and reversible. 2. Certain fractionated ginsenosides (Rb(1), Rb(2), Rc, Rf, Rg(2) and Ro) also produced an outward current in a concentration-dependent manner with the order of potency of Rf>Ro>Rb(1)=Rb(2)>Rg(2)>Rc. Other ginsenosides (Rd, Re and Rg(1)) had little or no effect. 3. The GTS effect was completely blocked by bath application of the Ca(2+)-activated Cl(-) channel blocker niflumic acid and by intracellular injection of the calcium chelator BAPTA or the IP(3) receptor antagonist heparin. Also, the effect was partially blocked by bath-applied U-73122, a phospholipase C (PLC) inhibitor and by intracellularly injected GTP gamma S, a non-hydrolyzable GTP analogue. Whereas, it was not altered by pertussin toxin (PTX) pretreatment. 4. These results indicate that: (1) interaction of ginsenosides with membrane component(s) at the extracellular side leads to Ca(2+)-activated Cl(-) channel opening in Xenopus oocyte membrane; and (2) this process involves PLC activation, the release of Ca(2+) from the IP(3)-sensitive intracellular store and PTX-insensitive G protein activation.
Choi
S
S
National Research Laboratory for the Study of Ginseng Signal Transduction, Department of Physiology, College of Veterinary Medicine, Chonnam National University, Kwangju 500-757, Korea.
Rho
S H
SH
Jung
S Y
SY
Kim
S C
SC
Park
C S
CS
Nah
S Y
SY
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002491:Central Nervous System Agents / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D018118:Chloride Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004347:Drug Interactions; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D036145:Ginsenosides; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D009865:Oocytes; D012503:Saponins / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014982:Xenopus laevis
D002491:Central Nervous System Agents; D002614:Chelating Agents; D018118:Chloride Channels; D004791:Enzyme Inhibitors; D036145:Ginsenosides; D012503:Saponins; D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D006493:Heparin; D010738:Type C Phospholipases; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium