Vasodilatory Effect ofPhellinus linteusExtract in Rat Mesenteric Arteries

Abstract

Phellinus linteusis a well-known medicinal mushroom that is widely used in Asian countries. In several experimental models,Phellinus linteusextracts were reported to have various biological effects, including anti-inflammatory, anti-cancer, hepatoprotective, anti-diabetic, neuroprotective, and anti-angiogenic activity. In the present study, several bioactive compounds, including palmitic acid ethyl ester and linoleic acid, were identified inPhellinus linteus. The intermediate-conductance calcium-activated potassium channel (IKCa) plays an important role in the regulation of the vascular smooth muscle cells' (VSMCs) contraction and relaxation. The activation of the IK(Ca)channel causes the hyperpolarization and relaxation of VSMCs. To examine whetherPhellinus linteusextract causes vasodilation in the mesenteric arteries of rats, we measured the isometric tension using a wire myograph. After the arteries were pre-contracted with U46619 (a thromboxane analogue, 1 mu M),Phellinus linteusextract was administered. ThePhellinus linteusextract induced vasodilation in a dose-dependent manner, which was independent of the endothelium. To further investigate the mechanism, we used the non-selective K(+)channel blocker tetraethylammonium (TEA). TEA significantly abolishedPhellinus linteusextract-induced vasodilation. Thus, we tested three different types of K(+)channel blockers: iberiotoxin (BK(ca)channel blocker), apamin (SK(ca)channel blocker), and charybdotoxin (IK(ca)channel blocker). Charybdotoxin significantly inhibitedPhellinus linteusextract-induced relaxation, while there was no effect from apamin and iberiotoxin. Membrane potential was measured using the voltage-sensitive dye bis-(1,3-dibutylbarbituric acid)-trimethine oxonol (DiBAC(4)(3)) in the primary isolated vascular smooth muscle cells (VSMCs). We found that thePhellinus linteusextract induced hyperpolarization of VSMCs, which is associated with a reduced phosphorylation level of 20 KDa myosin light chain (MLC20).