Effect of calmodulin on ginseng saponin-induced Ca2+-activated Cl- channel activation in Xenopus laevis oocytes.
We previously demonstrated the ability of ginseng saponins (active ingredients of Panax ginseng) to enhance Ca2+-activated Cl- current. The mechanism for this ginseng saponin-induced enhancement was proposed to be the release of Ca2+ from IP3-sensitive intracellular stores through the activation of PTX-insensitive Galpha(q/11) proteins and PLC pathway. Recent studies have shown that calmodulin (CaM) regulates IP3 receptor-mediated Ca2+ release in both Ca2+-dependent and -independent manner. In the present study, we have investigated the effects of CaM on ginseng saponin-induced Ca2+-activated Cl- current responses in Xenopus oocytes. Intraoocyte injection of CaM inhibited ginseng saponin-induced Ca2+-activated Cl- current enhancement, whereas co-injection of calmidazolium, a CaM antagonist, with CaM blocked CaM action. The inhibitory effect of CaM on ginseng saponin-induced Ca2+-activated Cl- current enhancement was dose- and time-dependent, with an IC50 of 14.9 +/- 3.5 microM. The inhibitory effect of CaM on saponin's activity was maximal after 6 h of intraoocyte injection of CaM, and after 48 h the activity of saponin recovered to control level. The half-recovery time was calculated to be 16.7 +/- 4.3 h. Intraoocyte injection of CaM inhibited Ca2+-induced Ca2+-activated Cl- current enhancement and also attenuated IP3-induced Ca2+-activated Cl- current enhancement. Ca2+/CaM kinase II inhibitor did not inhibit CaM-caused attenuation of ginseng saponin-induced Ca2+-activated Cl- current enhancement. These results suggest that CaM regulates ginseng saponin effect on Ca2+-activated Cl current enhancement via Ca2+-independent manner.
Lee
Jun-Ho
JH
Research Laboratory for the Study of Ginseng Signal Transduction, College of Veterinary Medicine, Konkuk University, Seoul 143-701, Korea.
Jeong
Sang-Min
SM
Lee
Byung-Hwan
BH
Kim
Jong-Hoon
JH
Ko
Sung-Ryong
SR
Kim
Seung-Hwan
SH
Lee
Sang-Mok
SM
Nah
Seung-Yeol
SY
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002147:Calmodulin / Q000494:pharmacology*; D018118:Chloride Channels / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects*; D008845:Microinjections; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D005894:Panax / Q000737:chemistry*; D012503:Saponins / Q000302:isolation & purification / Q000494:pharmacology*; D013997:Time Factors; D014982:Xenopus laevis
D002147:Calmodulin; D018118:Chloride Channels; D012503:Saponins; D002118:Calcium