The saponin monomer of dwarf lilyturf tuber, DT-13, reduces L-type calcium currents during hypoxia 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 effects of DT-13 on L-type calcium currents (ICa,L), exploring the mechanisms of DT-13's cardioprotective effects in the condition of pathophysiology, we directly measured the ICa,L during hypoxia in the adult rat cardiac myocytes exposed to DT-13 using standard whole-cell patch-clamp recording technique. Our previous results showed that DT-13 exerted decreasing effects on the ICa,L of the single adult rat cardiac myocytes. In the condition of hypoxia, the current density was inhibited by about 29% after exposure of the cells to DT-13 (0.1 μmol L− 1) for 10 min, from 6.96 ± 1.05 pA/pF to 4.38 ± 0.35 pA/pF (n = 5, P < 0.05). This ICa,L-inhibiting action of DT-13 was concentration-dependent and showed no frequency-dependence. DT-13 up-shifted the current–voltage (I–V) curve. Steady-state activation of ICa,L was not affected markedly, and the half activation potential (V0.5) in the presence of DT-13 (0.1 μmol L− 1) was also not significantly different. DT-13 at 0.1 μmol L− 1 markedly accelerated the voltage-dependent steady-state inactivation of calcium current and shifted the steady-state inactivation curve of ICa,L to the left. In combination with previous reports, these results suggest that there might be a close relationship between the cardioprotective effects of DT-13 and L-type calcium channels in the condition of hypoxia.