Ph.D. Candidacy Exam - Aortic and Microvascular Endothelial Calcium and Nitric Oxide Response to Shear Stress and the Role of Calcium in Nitric Oxide Production
Date: February 1, 2006
Time: 1:00 PM
Location: Bossone Research Enterprise Center, Room: 303
Dihui Hong, M.S.
Advisors: Kenneth A. Barbee, Ph.D., Donald G. Buerk, Ph.D. and Dov Jaron, Ph.D.
Background and Objectives:
Endothelial cells (ECs) are subject to the shear stress generated by blood flowing past their apical surfaces. Changes in fluid shear stress could be sensed directly by cells and elicit a cascade of responses which include the elevation of intracellular Ca2+ and production of nitric oxide (NO). Calcium is an essential trigger to a cascade of physiological and biochemical responses to shear stress and NO regulates several vascular functions such as vessel relaxation and inhibition of platelet aggregation. This study aims to quantify the relationship between shear stress and NO release; compare the calcium and NO response to shear stress between the ECs from large vessels and microvessels; and investigate the efficiency of calcium through a variety of different calcium channels in eNOS activation. Further extend this study to evaluate the role of calcium from various calcium channels in shear stress-induced NO release.
Preliminary research has focused on comparing the difference in calcium responses between macrovascular and microvascular endothelial cells in response to different levels of shear stress. In Bovine aortic endothelial cells( BAECs, macrovascular), the onset of shear stress elicited a transient increase in intracellular calcium concentration that was spatially uniform, synchronous, and dose dependent. In contrast, the response of rat adrenomedulary endothelial cells (RAMECs, microvascular) was heterogeneous in time and space. Shear stress induced calcium waves that originated from one or several cells and propagated to neighboring cells. The initiation and the propagation of calcium waves in RAMECs were significantly suppressed under conditions in which either purinergic receptors were blocked by suramin or extracellular ATP was degraded by apyrase. Exogenously applied ATP produced similarly heterogeneous responses. The preliminary results suggest that shear stress stimulates RAMECs to release ATP, causing the increase in intracellular calcium concentration via purinergic receptors in cells that are heterogeneously sensitive to ATP. The propagation of the calcium signal is also mediated by ATP, and the spatial pattern suggests a locally elevated ATP concentration in the vicinity of the initially responding cells. In addition to calcium studies, we also conducted experiments to quantitatively measure NO release from BAECs in response to different shear stresses using microelectrode positioned in a parallel flow chamber. The preliminary data in NO experiments suggest that NO production rate vary as a nonlinear function of shear stress.
The Bossone Research Enterprise Center is located at the corner of 32nd and Market Streets.