Electrical resistance and macromolecular permeability of retinal capillary endothelial cellsin vitro

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Abstract
This study was undertaken to examine the ability of retinal capillary endothelial cells to retain blood-retinal barrier properties in vitro. Second passage bovine retinal capillary endothelial cells were grown to confluence on polycarbonate filters in two chamber systems coated with laminin, fibronectin and type IV collagen. The electrical resistances, permeability of 3H-inulin and expression of blood-brain barrier related enzymes by retinal cells was observed and compared with bovine aortic endothelial cells and bovine fibroblasts. The electrical resistance of retinal cells rose over the first week of culture, peaking after 5–9 days in culture. In eleven separate experiments (n = 5 for each experiment) the average peak resistance of retinal endothelial cells ranged from 89.3–186.6 with a mean average of 129.0 ohm.cm2. In one of these experiments, the peak electrical resistance of retinal cells was 149.0 ± 10.3 compared with 34.8 ± 6.8 for aortic cells and 37.8 ± 3.8 ohm.cm2 for fibroblasts. The permeability coefficients of inulin were: retinal cells 0.17 ± 0.09, aortic cells 3.47 ± 1.58 (p = 0.015), fibroblasts 3.93 ± 0.78 (p = 0.002)×10-6 cm/sec. Retinal cells expressed significantly higher activities of γ-glutamyl transpeptidase and alkaline phosphatase than the other cell types. Treatment of the monolayers with the calcium ionophore, A23187, resulted in a reversible increase in permeability as has been described for peripheral vascular endothelium. We conclude that BRCEC retain at least some of their specialised barrier properties in vitro. This model may be useful for the study of retinal diseases characterized by increased permeability of the retinal microvascular endothelium, such as cystoid macular edema and diabetic retinopathy.