Sophocarpine Attenuates the Na+-dependent Ca2+ Overload Induced by Anemonia Sulcata Toxin—Increased Late Sodium Current in Rabbit Ventricular Myocytes

Abstract

Many studies indicate that an increase in late sodium current (I(Na.L)) of cardiomyocytes causes intracellular Na overload and subsequently raises the reverse Na/Ca exchanger current (INCX), ultimately resulting in intracellular Ca overload. Therefore, using drugs to inhibit the increased INa.L under various pathological conditions can lower intracellular Ca overload. This study was intended to explore the effect of sophocarpine (SOP) on the increase in INa.L, INCX, calcium transient and contraction in rabbit ventricular myocytes induced by Anemonia sulcata toxin II (ATX II), an opener of sodium channel, with the application of whole-cell patch-clamp techniques, the video-based motion edge detection system, and the intracellular calcium concentration determination system. The results indicate that tetrodotoxin (TTX, 4 μM ) obviously decreased INa.L and INCX enlarged by ATX II (30 nM), and SOP (20, 40, and 80 μM) also inhibited both the parameters concentration dependently in rabbit ventricular myocytes. However, transient sodium current remained unaffected by the above-mentioned concentrations of ATX II, TTX, and SOP. In addition, SOP also reversed diastolic calcium concentration, calcium transient amplitude, and ventricular muscle contractility augmented by ATX II. Its effects were similar to those of TTX, a specific inhibitor of the sodium channel. In conclusion, SOP inhibits INa.L, INCX, diastolic Ca concentration, and contractility in rabbit ventricular myocytes, which suggests that relief of intracellular Ca overload through inhibiting INa.L is likely to become a new therapeutic mechanism of SOP against arrhythmia and myocyte damage associated with intracellular Ca overload.