Effect of ginsenoside Rb1 on rat liver phosphoproteins induced by carbon tetrachloride.

We investigated the effects of ginsenoside Rb1 (G-Rb1), a major saponin from Panax ginseng C. A. MEYER, on rat liver protein phosphorylation after intraperitoneal administration of CCl4 alone or together with G-Rb1. We found that 118, 63, and 34kDa proteins were prominently phosphorylated in liver homogenates prepared from CCl4-administered rats, while these protein-phosphorylations were inhibited in the homogenate prepared from the G-Rb1 plus CCl4-administration group. When inhibitors of protein kinases were exogenously added to the homogenates from either the CCl4-administered group or the G-Rb1 plus CCl4-administered group, their phosphorylations were inhibited much more by W-7, an inhibitor of Ca2+/calmodulin-dependent protein kinase (CaM-PK), than by H-7, an inhibitor of protein kinase C (C-kinase). Interestingly, only 34kDa was phosphorylated in homogenates prepared from the corn oil-, G-Rb1-, and G-Rb1 plus CCl4-administered groups by the exogenous addition of sodium fluoride (NaF), an inhibitor of glycogen synthase. Additionally, G-Rb1 inhibited the Ca(2+)-accumulation induced by CCl4 both in liver homogenates and microsomes. The above results imply that G-Rb1 inhibits the CCl4-induced protein phosphorylations by modulating CaM-PK rather than C-kinase, and that 34kDa protein may play a different biological role in cellular environment from 118 and 63kDa proteins. Therefore, a study in which G-Rb1 is employed as a modulator of critical CCl4-induced phenomena ranging from the disturbance of Ca2+ concentration to protein phosphorylation may be successfully applicable to investigate the diverse physiological functions of liver.