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CARDIOVASCULAR

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

Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, People's Republic of China

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 Ca²⁺-activated potassium (BK_Ca) channel and on rat thoracic aortas. BK_Ca channels encoded with either (BK-) or / subunits (BK-+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-+1 currents with a half-maximal concentration (EC₅₀) of 0.8 nM and a Hill coefficient of 1.11 at 10 µMCa²⁺ and with an EC₅₀ of 12.6 nM and a Hill coefficient of 1.08 at 0 µMCa²⁺. Puerarin (1 nM) induced a 16-mV leftward shift in the conductance-voltage curve for BK-+1 currents at 10 µMCa²⁺ and at 100 nM induced a 26-mV leftward shift at 0 µMCa²⁺. Puerarin mainly increased the BK-+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 µM) caused concentration-dependent relaxations of rat thoracic aortic rings contracted with 1 µM noradrenaline bitartrate (EC₅₀ = 1.1 µM). 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-+1 channels. The activation of the BK_Ca channel probably contributes to the puerarin-mediated vasodilation action.

Address correspondence to: Xiang-Liang Yang, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China. E-mail: yangxl{at}mail.hust.edu.cn