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

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 μg ml −1 ) and reversible. 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. 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 GTPγS, a non‐hydrolyzable GTP analogue. Whereas, it was not altered by pertussin toxin (PTX) pretreatment. 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.British Journal of Pharmacology (2001) 132 , 641–648; doi: 10.1038/sj.bjp.0703856