Relaxation of Rat Aorta by Farrerol Correlates with Potency to Reduce Intracellular Calcium of VSMCs

Farrerol, isolated from Rhododendron dauricum L., has been proven to be an important multifunctional physiologically active component, but its vasoactive mechanism is not clear. The present study was performed to observe the vasoactive effects of farrerol on rat aorta and to investigate the possible underlying mechanisms. Isolated aortic rings of rat were mounted in an organ bath system and the myogenic effects stimulated by farrerol were studied. Intracellular Ca2+ ([Ca2+](in)) was measured by molecular probe fluo-4-AM and the activities of L-type voltage-gated Ca2+ channels (LVGC) were studied with whole-cell patch clamp in cultured vascular smooth muscle cells (VSMCs). The results showed that farrerol significantly induced dose-dependent relaxation on aortic rings, while this vasorelaxation was not affected by N-G-nitro-L-arginine methylester ester or endothelium denudation. In endothelium-denuded aortas, farrerol also reduced Ca2+-induced contraction on the basis of the stable contraction induced by KCl or phenylephrine (PE) in Ca2+-free solution. Moreover, after incubation with verapamil, farrerol can induce relaxation in endothelium-denuded aortas precontracted by PE, and this effect can be enhanced by ruthenium red, but not by heparin. With laser scanning confocal microscopy method, the farrerol-induced decline of [Ca2+] in in cultured VSMCs was observed. Furthermore, we found that farrerol could suppress Ca2+ influx via LVGC by patch clamp technology. These findings suggested that farrerol can regulate the vascular tension and could be developed as a practicable vasorelaxation drug.