Semester

Spring

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Pingnian He.

Abstract

The endothelial nitric oxide synthase (eNOS)-produced nitric oxide (NO) is best known to be essential in the regulation of vascular tone, blood flow and blood pressure. It remains unclear with respect to the functional roles and underlying mechanisms of eNOS activation and NO production in the regulation of increased microvessel permeability under inflammatory conditions. This dissertation was carried out to investigate the roles of eNOS and NO in the regulation of platelet activating factor (PAF), a typical inflammatory mediator, and hydrogen peroxide (H2O2), one of the reactive oxygen species-induced increases in microvessel permeability and to further elucidate the underlying mechanisms involved in NO-mediated permeability increases. Studies were conducted on individually perfused intact rat mesenteric venules to closely mimic the in vivo microvessel physiology. Combining functional measurements of changes in microvessel permeability with structural and cellular signaling studies via confocal and fluorescence imaging, we quantitatively demonstrated that caveolin-1 and endothelial Ca2+ concentration (EC [Ca2+]i) antagonistically regulate PAF-induced eNOS activation and NO production, and the overall amount of NO determines the magnitude of increases in microvessel permeability. At an individual endothelial cellular level, our results demonstrated that PAF-induced immediate and transient increases in microvessel permeability were associated with generalized endothelial gap formation, but the magnitude of gap formation varies among endothelial cells. The simultaneous measurement of PAF-induced EC [Ca 2+]i, NO production, and gap formation demonstrated a close linear relationship between each other, indicating that the variation in endothelial gap formation is attributed to the heterogeneous response in EC [Ca 2+]i, which determines the magnitude of downstream NO production at cellular levels. In contrast, H2O2 induced a much larger amount of endothelial NO production than that in PAF-perfused vessels, which instead of causing immediate and transient permeability increases, triggers vascular cell apoptosis, resulting in delayed and progressive increases in microvessel permeability. These data suggest that eNOS-derived NO exerts different actions in modulating microvessel barrier function, either through induction of endothelial gap formation to cause immediate and transient increases in microvessel permeability, or via initiation of vascular cell apoptosis to cause delayed and progressive permeability increases depending on the different stimuli under different pathological conditions.

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