Activation of Large-Conductance Calcium-Activated Potassium Channels by Puerarin: The Underlying Mechanism of Puerarin-Mediated Vasodilation

Abstract

Puerarin is the main isoflavone found in Pueraria lobata (Willd) Ohwi, which has been used in therapy for various cardiovascular diseases. The present study examined the effects of puerarin on the large-conductance voltage-and Ca 2ϩ -activated potassium (BK Ca ) channel and on rat thoracic aortas. BK Ca channels encoded with either ␣ (BK-␣) or ␣/␤ subunits (BK-␣ϩ␤1) were heterologously expressed in Xenopus oocytes or human embryonic kidney 293 cells. The activities of BK Ca channels were measured using excised patch-clamp recordings. Puerarin activated BK-␣ϩ␤1 currents with a half-maximal concentration (EC 50 ) of 0.8 nM and a Hill coefficient of 1.11 at 10 M Ca 2ϩ and with an EC 50 of 12.6 nM and a Hill coefficient of 1.08 at 0 M Ca 2ϩ . Puerarin (1 nM) induced a 16-mV leftward shift in the conductance-voltage curve for BK-␣ϩ␤1 currents at 10 M Ca 2ϩ and at 100 nM induced a 26-mV leftward shift at 0 M Ca 2ϩ . Puerarin mainly increased the BK-␣ϩ␤1 channel open probability without changing the unitary conductance. Activation was also detected in the absence of the ␤1 subunit. A deglycosylated analog of puerarin, daidzein, also activated BK Ca channels with weaker potency. In addition, puerarin (0.1 to 1000 M) caused concentration-dependent relaxations of rat thoracic aortic rings contracted with 1 M noradrenaline bitartrate (EC 50 ϭ 1.1 M). These were significantly inhibited by 50 nM iberiotoxin, a specific blocker of BK Ca channels. This is the first study demonstrating that puerarin activates BK Ca channels, especially BK-␣ϩ␤1 channels. The activation of the BK Ca channel probably contributes to the puerarin-mediated vasodilation action.

Cardiovascular Ion Channels as a Molecular Target of Flavonoids

“…Xu et al reported that kaempferol exerts part of its vasodilatory activity via activation of BK Ca channels [31]. Similar effects have been shown for the isoflavone puerarin [32]. Dioclein, a flavonoid isolated from the root of Dioclea grandiflora, a legume of the native Americans, causes hypotension in normotensive rats [33].…”

The anti-hypertensive effect of Danshen (Salvia miltiorrhiza) and Gegen (Pueraria lobata) formula in rats and its underlying mechanisms of vasorelaxation

“…Daidzein was also found to reduce the endothelial release of prostaglandin H 2 , a cyclooxygenase-derived vasoconstrictor (Vera et al, 2005). Puerarin, one of the active components of Gegen, was found to be involved in activating the large-conductance calcium-activated potassium channels (Sun et al, 2007). Despite evidence showing the individual vasodilative effect of Danshen and Gegen, the combined effect of DG on aorta was yet to be studied.…”

“…Besides, tanshinone II A , a lipophilic active ingredient of Danshen, could induce relaxation on rat coronary arteries and aorta through nitric oxide (NO)-mediated vasodilation (Kim et al, 2007;Wu et al, 2009) and was found to be K ATP channel-related . For Gegen, its active component daidzein, was shown to improve endothelial function in several studies (Mishra et al, 2000;Colacurci et al, 2005) and it induced vasodilation through NO-mediated mechanism (Mishra et al, 2000;Vera et al, 2005), and large-conductance calcium-activated potassium channels (Sun et al, 2007;Zhao et al, 2010), Kir channels Further investigations of the involvement of (a) inward rectifier potassium channels (BaCl2); (b) voltage-dependent potassium channels (4-AP); (c) ATP-sensitive potassium channels (glibenclamide) and (d) large conductance calcium-activated potassium channels (iberiotoxin, IbTX) in DG extract-induced relaxations of (a, b, and d) U46619 or (c) phenylephrine-precontracted aorta rings. The results were expressed as mean ± SEM (n = 6-8), with *p < 0.05 and **p < 0.01, using one-way ANOVA.…”

“…On the other hand, Gegen has the function of purging heat, improving the "yang qi", and detoxification. Gegen mainly consists of isoflavonoids such as puerarin, daidzin and diadzein which exhibited anti-hypertensive (Sun et al, 2007), and antithrombosis effects (Choo et al, 2002), as well as lowering plasma cholesterol (Yan et al, 2006).…”

Molecular Cloning and Functional Characterization of Two Divergent 4-Coumarate : Coenzyme A Ligases from Kudzu (<i>Pueraria lobata</i>)

“…1,2) Its pharmacological effects are due to the presence of isoflavonoids, which include puerarin, daidzin, and other related metabolites. Puerarin exhibits diverse medicinal properties including hypotensive, 3) hypolipidemic, 4) hypoglycemic, 5) anti-oxidant, 6) anti-ischaemia, 7) vasodilation 8) and estrogen-like effects. 9) As an isoflavonoid, the biosynthesis of puerarin should derive from phenylpropanoid metabolism, in which the enzymes in the early steps such as phenylalanine ammonia lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate : coenzyme A ligase (4CL), chalcone synthase (CHS), chalcone reductase (CHR), and chalcone isomerase (CHI) are conserved in many plant species.…”