Metformin improves IKCa-mediated endothelial dilative dysfunction of arteriole in diabetic rats
© Zhao et al; licensee BioMed Central Ltd. 2012
Published: 17 October 2012
Activation of intermediate conductance Ca2+-activated K+ channel (IKCa) in endothelial cells has been shown to contribute to vasodilation, especially in small vessels. The aim of this study is to observe the effect of metformin on endothelial dilative dysfunction in diabetic rats and investigate whether the alteration of IKCa are involved in the underlying mechanism.
Diabetic rat model was induced by a single intraperitoneal injection of 30 mg/kg STZ after high fat and glucose diet for 8 weeks. Animals whose blood glucose > 11.1 mmol/L were included in diabetic and metformin group. Age-matched animals fed with standard chow and injected with citric acid buffer were served as control. Four weeks after STZ injection, rats in three groups were fed with normal diet for additional 8 weeks. After that, fasting blood was drawn and third-order mesenteric arteries were separated. Hemoglobin A1c (HbA1c) was measured with an automatic analyzer. The changes of Ach- and NS309 (opener of IKCa and small conductance Ca2+-activated K+ channel, SKCa) -induced vasodilatation mediated by IKCa in mesentery arterioles of each group and mesentery arterioles of normal rats incubated with 200 μg/mL AGE-BSA (200 μg/mL BSA as control) for 3 hours were measured by multi-myograph system. The effect of metformin on AGE-BSA (200 μg/mL) and H2O2 (100 μmol/L) induced changes of IKCa mRNA and protein expression in cultured human umbilical vein endothelial cells (HUVECs) were detected by RT-PCR and Western blot. The level of malondialdehyde (MDA) and the activity of Cu-Zn superoxide dismutase (Cu-Zn SOD) in cellular supernatant were determined by colorimetric method.
Increased HbA1c level and reduceded endothelium-dependent dilative response mediated by IKCa in mesentery arterioles were observed in diabetic rats, and metformin treatment (300 mg/kg/day by gavage) restored the adverse condition. The vasodilatation mediated by IKCa was also impaired in 200 μg/mL AGE-BSA-incubated mesentery arterioles. AGE-BSA at 200 μg/mL concentration and H2O2 (100 μmol/L) significantly decreased the mRNA and protein expression of IKCa. AGE-BSA also increased the production of MDA and inhibited Cu-Zn SOD activity in HUVECs. Metformin of 10-6 mol/L and 10-7 mol/L reversed those effects.
Metformin significantly improves endothelium dilative dysfunction mediated by IKCa in diabetic rats, which is likely related to the inversion of AGEs-induced oxidation and downregulation of IKCa expression in endothelial cells.
This work was supported by the National Nature Science Foundation of China (grant number 81070129) and Nature Science Foundation of Shaanxi province (No. 2011JQ4021).
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