Metformin restores intermediate-conductance calcium-activated K⁺ channel- and small-conductance calcium-activated K⁺ channel-mediated vasodilatation impaired by advanced glycation end products in rat mesenteric arterys

The present study was designed to investigate the effect of metformin on the impairment of intermediate-conductance and small-conductance Ca²⁺-activated potassium channels (IK_Ca and SK_Ca)-mediated relaxation in diabetes and the underlying mechanism. The endothelial vasodilatation function of mesenteric arteries was assessed with the use of wire myography. Expression levels of IK_Ca and SK_Ca and phosphorylated Thr¹⁷² of AMP-activated protein kinase (AMPK) were measured using Western blot technology. The channel activity was observed using a whole-cell patch voltage clamp. Reactive oxygen species (ROS) were measured using dihydroethidium and 2′,7′-dichlorofluorescein diacetate. Metformin restored the impairment of IK_Ca- and SK_Ca-mediated vasodilatation in mesenteric arteries from streptozotocin-induced type 2 diabetic rats and that from normal rats incubated with advanced glycation end products (AGEs) for 3 hours. In cultured human umbilical vein endothelial cells (HUVECs), 1 μM metformin reversed AGE-induced increase of ROS and attenuated AGE- and H₂O₂- induced downregulation of IK_Ca and SK_Ca after long-term incubation (>24 hours). Short-term treatment (3 hours) with 1 μM metformin reversed the decrease of IK_Ca and SK_Ca currents induced by AGE incubation for 3 hours without changing the channel expression or the AMPK activation in HUVECs. These results are the first to demonstrate that metformin restored IK_Ca- and SK_Ca-mediated vasodilatation impaired by AGEs in rat mesenteric artery, in which the upregulation of channel activity and protein expression is likely involved.