Gintonin, a ginseng-derived lysophosphatidic acid receptor ligand, potentiates ATP-gated P2X(1) receptor channel currents

Abstract

Ginseng, the root of Panax ginseng C.A. Meyer, is used as a general tonic. Recently, we isolated a novel ginsengderived 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 ligandgated ion channels activated by extracellular ATP, and 7 receptor subtypes (P2X(1)-P2X(7)) have been identified. Most of the P2X(1) receptors are expressed in the smooth muscles of genitourinary organs involved in reproduction. A main characteristic of the P2X(1) receptor is rapid desensitization after repeated ATP treatment of cells or tissues expressing P2X(1) receptors. In the present study, we examined the effect of gintonin on P2X(1) receptor channel activity. P2X(1) receptors were heterologously expressed in Xenopus oocytes. ATP treatment of oocytes expressing P2X(1) receptors induced large inward currents (I (ATP) ), but repetitive ATP treatments induced a rapid desensitization of I (ATP) . Gintonin treatment after P2X(1) receptor desensitization potentiated I (ATP) in a concentration-dependent manner. We further examined the signaling transduction pathways involved in gintonin-mediated potentiation of I (ATP) . Gintoninmediated I (ATP) 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 P2X(1) receptor greatly attenuated the gintonin-mediated I (ATP) potentiation. These results indicate that G protein-coupled LPA receptor activation by gintonin is coupled to the potentiation of the desensitized P2X(1) receptor through a phosphoinositide-dependent pathway.