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 34 kDa 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 34 kDa 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 Ca²⁺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 34 kDa protein may play a different biological role in cellular environment from 118 and 63 kDa 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.