Quantitative Assessment of Capillary Permeability in Deep Intracardiac Capillaries Using Fluorescent Dextran

When the function of cardiac capillaries is impaired, cardiac function declines, and the risk of disease increases. No reliable assay has been developed to detect or evaluate the level of material exchange of capillaries deep within healthy heart tissue. In this study, we develop a new method to detect and evaluate molecules leaking from capillaries in cardiac tissue. By administering fluorescent dextran to mice via the tail vein, followed by rapid processing of the heart tissue, we have detected leaking fluorescent material from intracardiac microvessels. By comparing the detected images with those taken during the negative-control administration, using the image processing software LAS X and ImageJ, we detected trace amounts of fluorescent material that had leaked from the capillaries. We calculated the area of tissue where fluorescence was detected to perform a quantitative assessment, which we used as an indicator of capillary permeability. This new method of indexing will provide a different perspective on the factors contributing to the decline in cardiac function and the increased risk of disease with aging. Key features • A method to evaluate the permeability function of capillaries deep within healthy cardiac tissue has been developed using the diffusion area of a leaked fluorescent marker. • Evaluating the permeability function of deep tissues with dense capillary networks provides a foothold for elucidating the mechanisms of organ homeostasis, both maintenance and deterioration. • The diffusion of molecules into organs via capillary-to-cell exchange is an indicator of tissue function.