Gintonin a Ginseng-Derived Lysophosphatidic Acid Receptor Ligand Potentiates ATP-Gated P2X1 Receptor Channel Currents

摘要

Ginseng, the root of Panax ginseng C.A. Meyer, is used as a general tonic. Recently, we isolated a novel ginseng-derived lysophosphatidic acid (LPA) receptor ligand, gintonin. Gintonin activates G protein-coupled LPA receptors with high affinity in cells endogenously expressing LPA receptors, e.g., Xenopus oocytes. P2X receptors are ligand-gated ion channels activated by extracellular ATP, and 7 receptor subtypes (P2X1–P2X7) have been identified. Most of the P2X1 receptors are expressed in the smooth muscles of genitourinary organs involved in reproduction. A main characteristic of the P2X1 receptor is rapid desensitization after repeated ATP treatment of cells or tissues expressing P2X1 receptors. In the present study, we examined the effect of gintonin on P2X1 receptor channel activity. P2X1 receptors were heterologously expressed in Xenopus oocytes. ATP treatment of oocytes expressing P2X1 receptors induced large inward currents (IATP), but repetitive ATP treatments induced a rapid desensitization of IATP. Gintonin treatment after P2X1 receptor desensitization potentiated IATP in a concentration-dependent manner. We further examined the signaling transduction pathways involved in gintonin-mediated potentiation of IATP. Gintonin-mediated IATP potentiation was blocked by Ki16425, an LPA1/3 receptor antagonist, a PKC inhibitor, a PLC inhibitor, and a PI4-Kinase inhibitor but not by a calcium chelator. In addition, mutations of the phosphoinositide binding site of the P2X1 receptor greatly attenuated the gintonin-mediated IATP potentiation. These results indicate that G protein-coupled LPA receptor activation by gintonin is coupled to the potentiation of the desensitized P2X₁ receptor through a phosphoinositide-dependent pathway.