Cardiovascular diseases are currently the principal causes of morbidity and mortality in patients with diabetes mellitus and current therapy is still ineffective. Protein kinase C (PKC) is a key enzyme involved in endothelial dysfunction and decrease of vascular tissues potassium (K+) channels activity. Endothelium and K+ channels, in turn, are the main factors for maintenance of normal vasodilator potential at different pathological conditions, including diabetes. The aim of this study was to evaluate the effect of silencing of PKC-α and -δ genes using siRNA on endothelial dysfunction and potassium channelopathy in vascular smooth muscle cells (SMCs) at diabetes. Experimental design of the study comprised isolated rat aorta contractile recordings and whole-cell patch-clamp technique in isolated aortic SMCs. Dilator responses of vascular rings to acetylcholine (ACh, 10-9 – 10-5 M) were expressed as a percentage of the maximum contractile response produced by norepinephrine (10-6 M). Diabetes was induced by streptozotocin intraperitoneal injection to male Wistar rats (STZ, 65 mg/kg) and then verified by the presence of hyperglycaemia (glucose level was 30.05±0.51 mM, n=12, P<0.05) in 3d month after STZ injection and at the day of experiment. Diabetic rats were injected intravenously with siRNA targeted to PKC-α or -δ. Animals were killed on the 7th day by cervical dislocation following ketamine (45 mg/kg, i.p.) and xylazine (10 mg/kg, i.p.) anesthesia. The concentration-response curve to ACh in diabetic aortas precontracted with norepinephrine (10-6 M) was significantly shifted to the right (EC50 = 6.93±0.11, n=12, P<0.05 vs. 7.59±0.08, n=7 in control). Maximum dilatation to ACh in diabetic tissues was depressed (56.7±4.26%, n=12, P<0.05 vs. 96.5±3.05%, n=7 in control) PKC-α and -δ gene silencing led to significant restoration of ACh-induced dilatation in diabetic aortas with the maximum of 91± 2.11%, n=17; P>0.05 (EC50 = 7.58±0.07) for siRNA PKC-α, and 90.1±1.34 %, n=15, P<0.05 (EC50 = 7.9±0.1) for siRNA PKC-δ. In isolated diabetic aorta SMCs total outward K+ current was reduced (peak current density was 15.9 ± 0.9 pA/pF (n=13, P<0.05) as compared to control (55.6 ± 5.8 pA/pF, n=8). Aortic SMCs from animals treated with siRNA PKC-α showed significant increase in total K+ current in comparison to non-treated diabetic rats with peak density 23.5±1.9 pA/pF (n=12, P<0.05). The similar results were obtained in SMCs from animals treated with siRNA PKC-δ (23.9±2.7 pA/pF, n=7, P<0.05). In conclusion, the silencing of both PKC-α and -δ gene expression using siRNA led to increasing of total K+ outward current in vascular SMCs and restoring of endothelium-dependent vasodilatation in rats with diabetes mellitus. It is likely that siRNA technique can be a good therapeutic tool to normalize diabetic angiopathies.