The AMPK Activators AICAR and A769662 Reduce Relaxations of Rat Superior Mesenteric Arteries attributable to Endothelium-dependent Hyperpolarization

Introduction and Objective Adenosine monophosphate‐activated protein kinase (AMPK) has been reported to activate nitric oxide synthase to produce nitric oxide, which is one of the major vasodilator signals generated by endothelial cells, particularly in conduit arteries such as the aorta. However, small arteries play a more important role in regulating peripheral resistance. As the diameter of the arteries decreases, endothelium‐dependent hyperpolarization (EDH) becomes prominent in regulating the vascular tone. The signaling pathway of EDH varies with species and blood vessel type; nevertheless, an increase in extracellular potassium ion (K + ) level, due to activation of endothelial intermediate‐ and small‐conductance calcium‐activated potassium channels (IK Ca and SK Ca , respectively), is usually involved, with the resultant activation Na + /K + ‐ATPase and inwardly rectifying potassium channels in the underlying smooth muscle causing relaxation. 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‐weeks old Sprague Dawley (SD) rats were used. Superior mesenteric arteries were isolated and cut into rings, which were suspended in conventional organ chambers for isometric tension recording. To examine the signaling pathways involved, the rings were incubated with different pharmacological agents during 40 minutes, before exposing them to contracting and relaxing agents. Then, they were collected for measuring the activity of AMPK. Results Two AMPK activators with different structures and binding sites on the enzyme, AICAR (10 −4 M) and A769662 (10 −4 M), significantly reduced acetylcholine‐induced EDH‐like relaxations in superior mesenteric arteries of SD rats. SKA‐31 (opener of calcium‐activated potassium channels; 10 −5 M) induced relaxations which were also significantly inhibited by AICAR and A769662. The inhibitory effect of AICAR and A769662 was prevented by compound C (AMPK inhibitor; 10 −5 M). AMPK activity assays confirmed that AICAR and A769662 activated while compound C inhibited the activity of the kinase. Potassium ions (5×10 −3 M) induced relaxations in rings without endothelium which were not affected by AICAR but significantly inhibited by A769662. TRAM‐34 (10 −6 M) and UCL1684 (10 −6 M), blocker of IK Ca and SK Ca channels, respectively, alone did not affect acetylcholine‐induced relaxations; however, in combination with AICAR, the relaxations were significantly reduced. Conclusions Activation of endothelial and smooth muscle AMPK inhibits EDH‐like relaxations in the rat superior mesenteric artery. AICAR may inhibit endothelial calcium‐activated potassium channels to produce the inhibitory effect while A769662 inhibits the pathway downstream of smooth muscle hyperpolarization. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .