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.sup.-]) formation and concurrent impairment of voltage-dependent potassium ([K.sub.v]) channel function. However, it is unclear whether [ONOO.sup.-] plays a causative role in this impairment. We hypothesized that functional loss of [K.sub.v] channels in coronary smooth muscle cells (SMC) in diabetes is due to ONOO with subsequent tyrosine nitration of [K.sub.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.sup.-] in SCA from diabetic rats. IP and WB revealed elevated nitration of the [K.sub.v]1.2 [alpha]-subunit and reduced [K.sub.v]l.2 protein expression in diabetic rats. Each of these changes was improved in Eb-treated rats. Protein nitration and [K.sub.v]1.5 expression were unchanged in SCA from diabetic rats. Forskolin, a direct cAMP activator that induces [K.sub.v]1 channel activity, dilated SCA from nondiabetic rats in a correolide (Cor; a selective [K.sub.v]1 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.sub.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.sub.v]1 channel dysfunction in the coronary microcirculation. Eb may be beneficial for the therapeutic treatment of vascular complications in diabetes mellitus. diabetes; peroxynitrite; oxidative stress; coronary circulation