Wenxin Keli diminishes Ca2+ overload induced by hypoxia/reoxygenation in cardiomyocytes through inhibiting INaL and ICaL.

BACKGROUND: An increase in the late sodium current (INaL ) causes intracellular Na+ overload and subsequently intracellular Ca2+ ([Ca2+ ]i ) overload via the stimulated reverse Na+ -Ca2+ exchange (NCX). Wenxin Keli (WXKL) is an effective antiarrhythmic Chinese herb extract, but the underlying mechanisms are unclear. METHODS AND RESULTS: The INaL , NCX current (INCX ), L-type Ca2+ current (ICaL ), and action potentials were recorded using the whole-cell patch-clamp technique in rabbit ventricular myocytes. Myocyte [Ca2+ ]i transients were measured using a dual excitation fluorescence photomultiplier system. WXKL decreased the enhanced INaL , reverse INCX , diastolic [Ca2+ ]i , and the amplitude of Ca2+ transients induced by sea anemone toxin II (ATX II, a specific INaL channel opener) in a concentration-dependent manner. Hypoxia increased INaL , INCX , and diastolic [Ca2+ ]i , and decreased amplitude of [Ca2+ ]i transients. Hypoxia-reoxygenation aggravated these changes and induced spontaneous [Ca2+ ]i transients and hypercontraction in 86% cells (6/7). The application of WXKL during hypoxia or reoxygenation periods decreased the increased INaL , INCX , and diastolic [Ca2+ ]i , and prevented those events in 82% cells (9/11) under hypoxia-reoxygenation conditions. WXKL also inhibited the ICaL in a dose-dependent manner. Furthermore, WXKL shortened the action potential duration and completely abolished ATX II-induced early afterdepolarizations from 9/9 to /9. In isolated heart electrocardiogram recordings, WXKL inhibited ischemia-reperfusion induced ventricular premature beats and tachycardia. CONCLUSIONS: WXKL attenuated [Ca2+ ]i overload induced by hypoxia-reoxygenation in ventricular myocytes through inhibiting INaL and ICaL and prevents arrhythmias. This could, at least partly, contribute to the antiarrhythmic effects of WXKL.

The effect of ligustrazine on L-type calcium current, calcium transient and contractility in rabbit ventricular myocytes.

ETHNOPHARMACOLOGICAL RELEVANCE: Ligustrazine, the biologically active ingredient isolated from a popular Chinese medicinal plant, Ligusticum chuanxiong Hort. (Umbelliferae), has been used effectively to treat ischemic heart diseases, cerebrovascular and thrombotic vascular diseases since the 1970s. MATERIALS AND METHODS: At present, the effect of ligustrazine on L-type calcium current (I(Ca-L)) of ventricular myocytes remains controversial. In this study, we use the whole-cell patch-clamp techniques and video-based edge detection and dual excitation fluorescence photomultiplier systems to study the effects of ligustrazine on I(Ca-L), and calcium transient and contractility in rabbit ventricular myocytes in the absence and presence of isoprenaline (ISO). RESULTS: Ligustrazine (5 µM) in low concentration did not affect I(Ca-L) (P>0.05), higher concentrations of this drug (10, 20, 40, 80 µM) inhibited I(Ca-L) in a concentration-dependent manner and reduced I(Ca-L) by 9.6 ± 2.9%, 21.0 ± 4.3%, 33.9 ± 4.3%, and 51.6 ± 7.3%, respectively. Under normal conditions, ligustrazine (40 µΜ) reduced baseline of fura-2 fluorescence intensities (FFI, 340/380 ratio), namely diastolic calcium concentration, changes in FFI (ΔFFI, 340/380 ratio) and maximal velocity of Ca(2+) rise and decay (340/380 ratio/ms) by 6.3%, 26.1%, 25.2%, and 26.5%, and decreased sarcomere peak shorting (PS) and maximal velocity of shorting and relengthening by 36.4%, 31.9%, and 25.0%, respectively. Similarly, ligustrazine (40 µM) reduced baseline FFI, ΔFFI, and maximal velocity of Ca(2+) rise and decay by 14.1%, 51.1%, 35.2%, and 41.1%, and reduced sarcomere PS and maximal velocity of shorting and relengthening by 38.6%, 50.0% and 39.1%, respectively, in the presence of ISO. CONCLUSIONS: Ligustrazine not only significantly inhibits I(Ca-L) in a concentration-dependent manner but also suppressed calcium transient and contraction in the absence and presence of ISO.