Using micro‐PIV to interrogate the endothelial surface layer in arterioles in vivo

Abstract

The existence of a hydrodynamically relevant endothelial surface layer (ESL), ~ 0.5 μm in thickness, is well established in capillaries and venules in vivo. Since the ESL on vascular endothelial cells is likely to have broad implications for endothelial‐cell function, including mechanotransduction and vascular permeability, it is necessary to determine the extent to which the ESL is present on arteriolar endothelium. We applied microviscometric analysis to data obtained using micro‐particle image velocimetry (μ‐PIV) in cremaster‐muscle arterioles of wild‐type mice. Due to the puslatile nature of the flow in arterioles, data acquisition was triggered with the EKG at specific points in the cardiac cycle. Results from data taken at peak systole in the cardiac cycle show the existence of a hydrodynamically relevant ESL that is ~ 0.38 μm in thickness in arterioles 20–60 μm in diameter (n=18). This is compared with results from venules showing a hydrodynamically relevant ESL that is ~ 0.53 μm in thickness (n=23). We therefore conclude that there exists a significant ESL in arterioles that is thinner then that found in venules (p=0.055). Results from data obtained at four equally spaced points in the cardiac cycle show that the ESL thickness in arterioles does not fluctuate with flow variations arising from cardiac‐induced pulsatility (n=8). Supported by NIH grant R01 HL76499.