Ginsenosides regulate ligand-gated ion channels from the outside |
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Authors: | Lee Byung-Hwan Jeong Sang Min Ha Tal Su Park Chul-Seung Lee Jun-Ho Kim Jong-Hoon Kim Dong-Hyun Han Jin Su Kim Hyoung-Chun Ko Sung-Ryong Nah Seung-Yeol |
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Institution: | Research Laboratory for the Study of Ginseng Signal Transduction and Department of Physiology, College of Veterinary Medicine, Konkuk University, Seoul 143-701, Korea. |
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Abstract: | Treatment with ginsenosides, the major active ingredients of Panax ginseng, produces a variety of physiological effects on the central and peripheral nervous systems. Ginsenosides inhibit various types of ligand-gated ion channel but it is not clear whether they act from within or outside the cell since they are somewhat membrane-permeable. In the present study, we used the Xenopus oocyte gene expression system to determine from which side of the cell membrane the ginsenoside Rg3 (Rg3), and M4, a ginsenoside metabolite, act to regulate ligand-gated ion channel activity. Ligand-gated ion currents were measured using the two-electrode voltage clamp technique. Rg3 and M4 inhibited 5-HT3A and a3b4 nACh receptor-mediated ion currents when present outside of the cell but not when injected intracellularly. We also examined the effect of these agents on oocytes expressing the gustatory cGMP-gated ion channel, which is known to have a cGMP binding site on the intracellular side of the plasma membrane and is only activated by cytosolic cGMP. Rg3 inhibited cGMP-gated ion currents when applied extracellularly or to an outside-out patch clamp, but not when injected into the cytosol or when using an excised inside-out patch clamp. These results indicate that Rg3 and M4 regulate ligand-gated ion channel activity from the extracellular side. |
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