Ebselen reduces nitration and restores voltage-gated potassium channel function in small coronary arteries of diabetic rats

Small coronary arteries (SCA) from diabetic rats exhibit enhanced peroxynitrite (ONOO^-) formation and concurrent impairment of voltage-dependent potassium (K_v) channel function. However, it is unclear whether ONOO^- plays a causative role in this impairment. We hypothesized that functional loss of K_v channels in coronary smooth muscle cells (SMC) in diabetes is due to ONOO^- with subsequent tyrosine nitration of K_v channel proteins. Diabetic rats and nondiabetic controls were treated with or without ebselen (Eb) for 4 wk. SCA were prepared for immunohistochemistry (IHC), immunoprecipitation (IP) followed by Western blot (WB), videomicroscopy, and patch-clamp analysis. IHC revealed excess ONOO^- in SCA from diabetic rats. IP and WB revealed elevated nitration of the K_v1.2 α-subunit and reduced K_v1.2 protein expression in diabetic rats. Each of these changes was improved in Eb-treated rats. Protein nitration and K_v1.5 expression were unchanged in SCA from diabetic rats. Forskolin, a direct cAMP activator that induces K_v1 channel activity, dilated SCA from nondiabetic rats in a correolide (Cor; a selective K_v1 channel blocker)-sensitive fashion. Cor did not alter the reduced dilation to forskolin in diabetic rats; however, Eb partially restored the Cor-sensitive component of dilation. Basal K _v current density and response to forskolin were improved in smooth muscle cells from Eb-treated DM rats. We conclude that enhanced nitrosative stress in diabetes mellitus contributes to K_v1 channel dysfunction in the coronary microcirculation. Eb may be beneficial for the therapeutic treatment of vascular complications in diabetes mellitus.