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

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. At present, the effect of ligustrazine on L-type calcium current (ICa-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 ICa-L, and calcium transient and contractility in rabbit ventricular myocytes in the absence and presence of isoprenaline (ISO). Ligustrazine (5μM) in low concentration did not affect ICa-L (P>0.05), higher concentrations of this drug (10, 20, 40, 80μM) inhibited ICa-L in a concentration-dependent manner and reduced ICa-L by 9.6±2.9%, 21.0±4.3%, 33.9±4.3%, and 51.6±7.3%, respectively. Under normal conditions, ligustrazine (40μΜ) 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 Ca2+ rise and decay (340/380ratio/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 (40μM) reduced baseline FFI, ΔFFI, and maximal velocity of Ca2+ 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. Ligustrazine not only significantly inhibits ICa-L in a concentration-dependent manner but also suppressed calcium transient and contraction in the absence and presence of ISO. (A) Ligustrazine inhibits ICa-L in a concentration dependent manner in rabbit ventricular myocytes. Currents were elicited by a 200ms depolarizing pulse applied at 0.5Hz from a holding potential of –80mV, in 10mV increments between –40 and +40mV. Ligustrazine (5μM) does not affect ICa-L, higher concentrations of this drug (10, 20, 40, 80μM) inhibit ICa-L in a concentration dependent manner. (B) Ligustrazine suppress cell shortening and calcium transients in rabbit ventricular myocytes under normal condition. Video-based edge detection and dual excitation fluorescence photomultiplier system (IonOptix) were used to record cell contraction and cal