Selective modulation of L-type calcium current by magnesium lithospermate B in guinea-pig ventricular myocytes

Magnesium lithospermate B (MLB) is the main water-soluble principle of Salviae Miltiorrhizae Radix (also called as ‘Danshen’ in the traditional Chinese medicine) for the treatment of cardiovascular diseases. MLB was found to possess a variety of pharmacological actions. However, it is unclear whether and how MLB affects the cardiac ion channels. In the present study, the effects of MLB on the voltage-activated ionic currents were investigated in single ventricular myocytes of adult guinea pigs. MLB reversibly inhibited L-type Ca2+ current (ICa,L). The inhibition was use-dependent and voltage-dependent (the IC50 value of MLB was 30 μM and 393 μM, respectively, at the holding potential of − 50 mV and − 100 mV). In the presence of 100 μM MLB, both the activation and steady-state inactivation curves of ICa,L were markedly shifted to hyperpolarizing membrane potentials, whereas the time course of recovery of ICa,L from inactivation was not altered. MLB up to 300 μM had no significant effect on the fast-inactivating Na+ current (INa), delayed rectifier K+ current (IK) and inward rectifier K+ current (IK1). The results suggest that the voltage-dependent Ca2+ antagonistic effect of MLB work in concert with its antioxidant action for attenuating heart ischemic injury.