Effects of ginsenosides on Ca channels and membrane capacitance in rat adrenal chromaffin cells

We investigated the effects of ginseng total saponins (GTS) and five ginsenosides on voltage-dependent Ca²⁺ channels and membrane capacitance using rat adrenal chromaffin cells. In this study, cells were voltage-clamped in a whole-cell recording mode and a perforated patch-clamp technique was used. The inward Ca²⁺ currents (I_Ca) was elicited by depolarization and the change in cell membrane capacitance (ΔC_m) was monitored. The application of GTS (100 μg/ml) induced rapid and reversible inhibition of the Ca²⁺ current by 38.8 ± 3.6% (n = 16). To identify the particular single component that seems to be responsible for Ca²⁺ current inhibition, the effects of five ginsenosides (ginsenoside Rb₁, Rc, Re, Rf, and Rg₁) on the Ca²⁺ current were examined. The inhibitions to the Ca²⁺ current by Rb₁, Rc, Re, Rf, and Rg₁ were 15.3 ± 2.2% (n = 5); 36.9 ± 2.4% (n = 7); 28.1 ± 1.9% (n = 12); 19.0 ± 2.5% (n = 10); and 16.3 ± 1.6% (n = 15), respectively. The order of inhibitory potency (100 μM) was Rc > Re > Rf > Rg₁ > Rb₁. A software based phase detector technique was used to monitor membrane capacitance change (ΔC_m). The application of GTS (100 μg/ml) induced inhibitory effects on ΔC_m by 60.8 ± 9.7% (n = 10). The inhibitions of membrane capacitance by Rb₁, Rc, Re, Rf, and Rg₁ were 35.3 ± 5.5% (n = 7); 41.8 ± 7.0% (n = 8); 40.5 ± 5.9% (n = 9); 51.2 ± 7.6% (n = 9); and 35.9 ± 5.1% (n = 10), respectively. The inhibitory potencies of the ginsenosides on ΔC_m were Rf > Rc > Re > Rg₁ > Rb₁. Therefore, we found that GTS and ginsenosides exerted inhibitory effects on both Ca²⁺ currents and ΔC_m in rat adrenal chromaffin cells. These results suggest that ginseng saponins regulate catecholamine secretion from adrenal chromaffin cells and this regulation could be the cellular basis of antistress effects induced by ginseng.