Diabetes is well known as a complex syndrome which leads to multiple malfunctions including vascular abnormalities. Changes in myofilament Ca2+-sensitivity plays a crucial role in complex interplay in contraction/dilation of vascular smooth muscle (SM) cells in diabetes which, in turn, alters protein kinase C (PKC) related mechanisms of Ca2+- signaling. In this study we have compared SM contractility and intracellular Ca2+ concentration ([Ca]i) in three groups of rats: streptozotocin-induced diabetes rats (STZ), STZ PKC-δ isozyme gene silencing rats and control group of animals) during activation of SM with cumulative doses of phenylephrine (PE, 10-9 -10-6 M). Animals were killed by cervical dislocation following ketamine (45 mg/kg, i.p.) and xylazine (10 mg/kg, i.p.) anesthesia on 3rd month of diabetes and on the 7th day after intravenous injection of siRNAs. Annealed siRNAs were injected (40 mkg / per rat) twice via tail vein with 24 hours interval. All animal studies were approved by the Institutional Animal Care and Use Committee. Thoracic aortas obtained from of male Wistar rats (250-300 g) were cut into 1,5 mm-wide rings and loaded with 10 µM Fura 2-AM for 4 hours. The results of [Ca]i measurements were presented as the ratio (R) of a 510-nm emission fluorescence intensity at 340- nm and 380-nm excitation signals. The sensitivity of contractile myofilaments to Ca2+ was measured as relationship between contractile force and R340/380 (ΔF/ΔR) . Low concentration (10-9 M) of PE provoked asynchronous phasic contractions and increase in [Ca]i which was followed by Ca2+-oscillations in STZ group likely due to over-activation in alpha-agonist stimulation while intact SM were without response to low PE concentration. ΔF/ΔR was significantly increased in STZ group up to 0.38±0.01 vs 0.21±0.02 in a control (n=12, P<0.05), suggesting that myofilaments sensitivity to calcium had increased under diabetes. sRNAs administration and following PKC-δ isozyme gene silencing restored normal SM sensitivity to alpha-agonist and normalized myofilament Ca sensitivity in STZ rats (ΔF/ΔR =0.23±0.03 in STZ PKC-δ group vs to a control (n=12, P>0.05), In conclusion, the data obtained clearly indicate an increased sensitivity of vascular SM to alpha-agonist stimulation as well an increment in sensitivity of contractile proteins to calcium in diabetic rats. The ability of siRNAs targeted to PKC-δ gene normalize Ca2+ signaling and vascular abnormalities supports PKC involvement in diabetic angiopathy development.