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KMID : 0578320110310020133
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Molecules and Cells
2011 Volume.31 No. 2 p.133 ~ p.140
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Ginsenoside Rg3 Enhances Large Conductance Ca2+-Activated Potassium Channel Currents: A Role of Tyr360 Residue
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Choi Sun-Hye
Shin Tae-Joon
Lee Byung-Hwan
Hwang Sung-Hee
Lee Sang-Mok
Lee Byung-Cheol
Park Cheol-Seung
Ha Tal-Soo
Nah Seung-Yeol
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Abstract
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Ginsenosides, active ingredients of Panax ginseng, are known to exhibit neuroprotective effects. Large-conduc-tance Ca2+-activated K+ (BKCa) channels are key modula-tors of cellular excitability of neurons and vascular smooth muscle cells. In the present study, we examined the effects of ginsenosides on rat brain BKCa (rSlo) channel activity heterologously expressed in Xenopus oocytes to elucidate the molecular mechanisms how ginsenoside regulates the BKCa channel activity. Ginsenoside Rg3 (Rg3) enhanced outward BKCa channel currents. The Rg3-enhancement of outward BKCa channel currents was concentration-depen-dent, voltage-dependent, and reversible. The EC50 was 15.1±3.1 μM. Rg3 actions were not desensitized by repeated treatment. Tetraetylammonium (TEA), a K+ channel blocker, inhibited BKCa channel currents. We examined whether extracellular TEA treatment could alter the Rg3 action and vice versa. TEA caused a rightward shift of the Rg3 con-centration-response curve (i.e., much higher concentration of Rg3 is required for the activation of BKCa channel compared to the absence of TEA), while Rg3 caused a rightward shift of the TEA concentration-response curve in wild-type channels. Mutation of the extracellular TEA binding site Y360 to Y360I caused a rightward shift of the TEA concentration-response curve and almost abolished both the Rg3 action and Rg3-induced rightward shift of TEA concentration-response curve. These results indicate that Tyr360 residue of BKCa channel plays an important role in the Rg3-enhancement of BCa channel currents.
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KEYWORD
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BKca channel, Ginsenoside Rg3, interaction site, Panax ginseng
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