Aquaporin-1 contribution to rat aortic endothelial hydraulic conductivity and how chronic transmural pressure affects it.

摘要

Hypertension is a slow-developing disorder which predisposes to cardiovascular disorders, including atherosclerosis. The initiating events of atherosclerosis begin with pressure-driven transport of low-density lipoprotein (LDL) cholesterol from the blood into the arterial intima around rare isolated sites of tight junction disruptions. Water further advects these particles in the subendothelial space where lesion formation is known to occur. In this thesis we seek to understand the nature and control of this water flux in greater detail and its influence on lipid transport into the wall, specifically in the presence of hypertension. We accomplish this by measuring the differential contribution of water transport across intercellular junctions to that through membrane bound aquaporin-1 (AQP1) water channels. The hydraulic conductivity (Lp) of excised rat aortas is measured before and after AQP1 inhibition by HgCl 2, as a function of transmural pressure (DeltaP). We observed a decrease in Lp at all three pressures upon AQP blocking, with the most dramatic effect at P = 60 mmHg, where Lp decreased by 32%. At this pressure, AQP blocking decreases the endothelial Lp (Lpe+i) 56% from 6.85 to 3.04 x 10 -8 cm·s-1˙mmHg-1. HgCl 2 blocking was also tested in vitro by measuring water flux across bovine aortic endothelial cell (BAEC) monolayers. The fractional contribution of AQPs to endothelial Lp was 22% in vitro compared to 31% in our ex vivo model. Lastly, we investigated the ability of the vessel to actively regulate their Lpe+i in response to chronic changes in transmural pressure. The average endothelial Lp of both SHR and 2K1C were both larger than their normotensive controls. The 2K1C endothelium contributed an average of 26% of the total wall resistance across the entire range, whereas its normotensive controls averaged 43%. Blocking AQPs severely increased the resistance (or the force per unit area) of the endothelium causing Lpe+i to drop 79% at P = 60 mmHg, implying the expression of AQPs is greater in hypertensive vessels. Understanding the enhanced water flux through hypertensive vessels will shed light on why chronic changes in pressure accelerates the progression of atherosclerotic lesion formation.