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

Abstract

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 Ca 2+ current ( I Ca,L). The inhibition was use-dependent and voltage-dependent (the IC 50 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 I Ca,L were markedly shifted to hyperpolarizing membrane potentials, whereas the time course of recovery of I Ca,L from inactivation was not altered. MLB up to 300 μM had no significant effect on the fast-inactivating Na + current ( I Na), delayed rectifier K + current ( I K) and inward rectifier K + current ( I K1). The results suggest that the voltage-dependent Ca 2+ antagonistic effect of MLB work in concert with its antioxidant action for attenuating heart ischemic injury.