| Summary: | 碩士 === 國立中正大學 === 化學工程所 === 93 === Angiotensin II (Ang II) is one of the atherosclerotic risk factors, which increases cytosolic calcium concentration via inositol 1,4,5-trisphosphate (IP3) signal pathway in vascular smooth muscle cells (SMCs), resulting in cell contraction. In addition, Ang II can also raise the level of intracellular superoxide anion (O2-) via NAD(P)H oxidase. Nitric oxide (NO) has been shown to inhibit mobilization of IP3-gated calcium channel through increased intracellular cyclic guanine monophosphate (cGMP). Furthermore, we have previously demonstrated that superoxide determines the SMC-NO uptake rate. Therefore, it is likely that Ang II may use O2- to increase the SMC-NO uptake rate, which may in turn serve as a negative feedback circuitry of calcium response. To demonstrate the role of superoxide in the Ang II-elicited calcium response, first we demonstrated that the calcium response is in an Ang II dependent manner using fluorescent dye, Fura-2, with a fluorescence spectrophotometer. After verifying the assay for calcium response, we had SMCs compete with oxyhemoglobin for NO during the Ang II challenge. Pretreatment of SMCs with NADPH or SOD inhibitors decreases the Ang II-elicited calcium response. In contrary, pretreatment of tiron, a superoxide scavenger, increases the Ang II-elicited calcium response. Taken together, our results demonstrate that superoxide in smooth muscle cells modulates negatively the Ang II-elicited calcium response via increasing the SMC-NO uptake, suggesting the beneficial role of superoxide in SMCs in the blood vessel response.
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