Regulation of vascular permeability in cell culture

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Abstract
Although one of the earliest findings of diabetic retinopathy is altered capillary permeability, metabolic factors in diabetes that may increase the permeability of capillaries to fluorescein are unknown. We have studied the effect of a variety of vascular and retinal cells and hyperglycemia on the diffusion rate of fluorescein. These studies were performed with a cell culture system that mimics the cross-section of a capillary by having two chambers separated with a porous membrane that can support the growth of cells on either side of the membrane. The addition of a confluent layer of endothelial cells or retinal pigmented epithelial (RPE) cells inhibited fluorescein diffusion between the two chambers 20- and 300-fold, respectively, after cells were cultured for >5 days. Exposure of endothelial cells to 400 mg/dl glucose for either 3 or 100 days did not affect the barrier function of these cells. The barrier function of capillary endothelial cells isolated from BB rats with chronic diabetes and from nondiabetic animals did not differ. In contrast to endothelial cells and RPE cells, arterial smooth muscle and pericytes, which are not known to form tight junctions, did not inhibit the diffusion of fluorescein more than 2-fold. Surprisingly, the dual culture of endothelial cells with either retinal pericytes or smooth muscle cells resulted in a 50-fold increase in the rate of fluorescein diffusion, showing a disruption of the endothelial barrier. In summary, the intercellular connections between endothelial and epithelial cells that are responsible for the barrier to fluorescein diffusion are not functionally affected by chronic exposure to hyperglycemia or diabetic conditions. The interaction between endothelial cells with capillary pericytes is important in maintaining vascular permeability and may be altered in the diabetic state.