Inhibitory effects of cytosolic ca2+ concentration by ginsenoside Ro are dependent on phosphorylation of IPI and dephosphorylation of ERK in Human platelets

Abstract

Intracellular Ca2+ ([ Ca 2+ ] i) is platelet aggregation-inducing molecule and is involved in activation of aggregation associated molecules. This study was carried out to understand the Ca2+-antagonistic effect of ginsenoside Ro (G-Ro), an oleanane-type saponin in Panax ginseng. G-Ro, without affecting leakage of lactate dehydrogenase, dose-dependently inhibited thrombin-induced platelet aggregation, and the half maximal inhibitory concentration was approximately 155 M. G-Ro inhibited strongly thrombin-elevated [ Ca 2+ ] i, which was strongly increased by A-kinase inhibitor Rp-8-Br-cAMPS compared to G-kinase inhibitor Rp-8-Br-cGMPS. G-Ro increased the level of cAMP and subsequently elevated the phosphorylation of inositol 1, 4, 5-triphosphate receptor I (IPI) (Ser1756) to inhibit [ Ca 2+ ] i mobilization in thrombin-induced platelet aggregation. Phosphorylation of IPI (Ser1756) by G-Ro was decreased by PKA inhibitor Rp-8-Br-cAMPS. In addition, G-Ro inhibited thrombin-induced phosphorylation of ERK 2 (42 kDa), indicating inhibition of Ca2+ influx across plasma membrane. We demonstrate that G-Ro upregulates cAMP-dependent IPI (Ser1756) phosphorylation and downregulates phosphorylation of ERK 2 (42 kDa) to decrease thrombin-elevated [ Ca 2+ ] i, which contributes to inhibition of ATP and serotonin release, and p-selectin expression. These results indicate that G-Ro in Panax ginseng is a beneficial novel Ca2+-antagonistic compound and may prevent platelet aggregation-mediated thrombotic disease.