Digital imaging system and virtual instrument platform for measuring hydraulic conductivity of vascular endothelial monolayers

We have developed an automated, digital imaging system, controlled by two virtual instruments, to measure hydraulic conductivity (L_p) of cultured endothelial monolayers. Live digital images of multiple independent experiments were captured by custom-designed video processing software running in National Instruments LabVIEW 6.1. Fluid displacement data are automatically displayed in real time as both volumetric flux (J_v) and hydraulic conductivity (L_p). A separate data analysis program is used to display permeability values from stored displacement measurements and displays J_v or L_p of each monolayer. Optional statistical filters have been included to aid in data analysis. This new digital permeability system is able to measure flux rates over a dynamic range from 10^-9 cm/s/cm H₂O to 10^-4 cm/s/cm H₂O. Values obtained for cultured lung microvascular L_p are nearly identical to other cultured endothelial monolayers and also to values obtained in-vivo using the Landis-Michel technique and the split-drop method. The use of a commercially available platform allows the system configuration to be easily modified to suit the experimental needs. The technical development of this system is described in detail.