Magnesium isoglycyrrhizinate inhibits L-type Ca2+ channels, Ca2+ transients, and contractility but not hERG K+ channels

To explore the cardiovascular protective effects of Magnesium isoglycyrrhizinate (MI), especially the underlying cellular mechanisms related to L-type calcium channels and myocardial contractility, and to examine the effects of MI on hERG K+ current expressed in HEK293 cells. We used the whole-cell patch clamp technique, video-based edge detection and dual excitation fluorescence photomultiplier systems to explore the effect of MI on L-type Ca2+ currents (ICa-L) and cell contraction in rat cardiomyocytes. We also examined the rapidly activating delayed rectifier potassium current (I-Kr) expressed in HEK293 cells using a perforated patch clamp. MI inhibited ICa-L in a dose-dependent manner, with a half-maximal inhibitory concentration (IC50) of 0.22 mg/ml, and the maximal inhibitory effect was 61.10 +/- 0.59%. MI at a concentration of 0.3 mg/ml reduced cell shortening by 24.12 +/- 3.97% and the peak value of the Ca2+ transient by 36.54 +/- 4.96%. MI had no significant influence on hERG K+ channels expressed in HEK293 cells at all test potentials. MI exerts protective effects on the heart via the inhibition of ICa-L and cell shortening in rat cardiomyocytes. However, MI had no significant influence on I-Kr; thus, MI may exert cardioprotective effects without causing drug-induced long QT syndrome.