Glycyrretinic acid blocks cardiac sodium channels expressed in Xenopus oocytes

Licorice has been used to treat many ailments including cardiovascular disorders in China for long time . Recent studies have shown that the cardiac actions of licorice have been attributed to its active component, glycyrretinic acid (GA). However, its mechanism remains poorly understood. The effects of GA on the cardiac sodium currents ( I Na), L-type calcium currents ( I Ca,L) and hyperpolarization-activated inward currents ( I f) were investigated. Human isoforms of wild-type and ΔKPQ-mutant type sodium channels were expressed in Xenopus oocytes, and the resulting currents (peak and late I Na) were recorded using a two-microelectrode voltage-clamp technique. A perforated patch clamp technique was employed to record I Ca,L and I f from isolated rabbit sinoatrial node pacemaker cells. GA inhibited peak I Na (33% at 90 μM) and late I Na (72% at 90 μM), but caused no significant effects on I Ca,L and I f. GA blocked cardiac sodium currents, particularly late I Na. Our findings might help to understand the traditional use of licorice in the treatment of cardiovascular disorders, because reduction of sodium currents (particularly late I Na) would be expected to provide protection from Na +-induced Ca 2+ overload and cell damage.