Role of AMPK in EDH-like relaxations in rat superior mesenteric arteries

Abstract

Introduction and Objective: Adenosine monophosphate-activated protein kinase (AMPK) has beneficial effects on the vasculature, including facilitation of vasodilatation. Endothelium-derived hyperpolarization (EDH) is one of the major vasoactive signals generated by endothelial cells for the regulation of vascular tone, in particular in resistance arteries which contribute to arterial blood pressure regulation. Although the mechanism underlying EDH varies with species and blood vessel type, activation of intermediate- and smallconductance calcium-activated potassium channels (IKCa and SKCa, respectively) in the endothelium followed by stimulation of Na+/K+-ATPase and inwardly-rectifying potassium channels (Kir) in the underlying vascular smooth muscle, is a common characteristic of the EDH pathway. The present study aimed to examine whether or not AMPK affects EDH-mediated relaxations and, if so, to determine the mechanism(s) involved. Methods: Male twelve-week-old Sprague Dawley (SD) rats were used. Superior mesenteric arterial rings were suspended in conventional organ chambers for isometric tension recording and were collected for measuring the activity of AMPK. Results: AICAR (AMPK activator; 10-4 M) significantly reduced acetylcholineinduced EDH-like relaxations in superior mesenteric arteries of SD rats; the effect was restored by compound C (AMPK inhibitor; 10-5 M). AMPK activity assays confirmed that AICAR (10-4 M) caused AMPK activation in SD rat mesenteric arteries. Ouabain (inhibitor of Na+/K+-ATPase; 10-3 M), but not barium chloride (inhibitor of Kir; 3 x 10-5 M), significantly reduced acetylcholine-induced EDH-like relaxations. The inhibitory effects of ouabain and AICAR on EDH-like relaxations were not additive. Similar results were obtained with endothelium-dependent relaxations induced by SKA-31 (positive allosteric modulator of SKCa and IKCa channels; 10-5 M). In rings without endothelium, potassium chloride (5 x 10-3 M)-induced relaxations were abolished by ouabain but were not affected by AICAR. Conclusions: Activation of AMPK reduces EDH-like relaxations in the rat superior mesenteric artery, likely by inhibiting, at the endothelial level, the IKCa-Na+/K+-ATPase signaling pathway.