ELECTRICAL-RESISTANCE AND MACROMOLECULAR PERMEABILITY OF RETINAL CAPILLARY ENDOTHELIAL-CELLS IN-VITRO

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 w ith laminin, fibronectin and type IV collagen. The electrical resistan ces, permeability of H-3-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 resis tance of retinal cells rose over the first week of culture, peaking af ter 5-9 days in culture. In eleven separate experiments (n = 5 for eac h experiment) the average peak resistance of retinal endothelial cells ranged from 89.3-186.6 with a mean average of 129.0 ohm.cm(2). 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.cm(2) 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)X10(-6) cm/sec. Reti nal cells expressed significantly higher activities of gamma-glutamyl transpeptidase and alkaline phosphatase than the other cell types. Tre atment of the monolayers with the calcium ionophore, A23187, resulted in a reversible increase in permeability as has been described for per ipheral vascular endothelium. We conclude that BRCEC retain at least s ome of their specialised barrier properties in vitro. This model may b e useful for the study of retinal diseases characterized by increased permeability of the retinal microvascular endothelium, such as cystoid macular edema and diabetic retinopathy.