Effects of Saponin Monomer 13 of Dwarf Lilyturf Tuber on L-Type Calcium Currents in Adult Rat Ventricular Myocytes

The saponin monomer 13 of dwarf lilyturf tuber (DT-13), one of the saponin monomers of dwarf lilyturf tuber, has been found to have potent cardioprotective effects. In order to investigate the effect of DT-13 on L-type calcium currents (I(Ca,L)), exploring the mechanisms of DT-13's cardioprotective effects, we directly measured the I(Ca,L) in the adult rat cardiac myocytes exposed to DT-13 using standard whole-cell patch-clamp recording technique. Our results showed that DT-13 exerted inhibitory effects on the I(Ca,L) of the single adult rat cardiac myocytes. The current density was reduced by about 38% after exposure of the cells to DT-13 (0.1 microM) for 10 minutes, from the control value of 7.46 +/- 1.31 pA/pF to 4.25 +/- 0.35 pA/pF (n = 6, p < 0.05). This I(Ca,L)-inhibiting action of DT-13 was concentration-dependent. DT-13 up-shifted the current-voltage (I-V) curve, but did not significantly affect the half activation potential (V0.5). V0.5 was from -11.8 +/- 0.9 mV in the control to -12.6 +/- 1.9 mV in the presence of DT-13 at 0.1 micromol/L. DT-13 at 0.1 microM did not markedly affect the activation of I(Ca,L), but shifted the inactivation curve of I(Ca,L) to the left. In combination with previous reports, these results suggest that there might be a close relationship between the cardioprotective effects of dwarf lilyturf tuber and the inhibitory effects of DT-13 on L-type calcium currents.