Serum inhibits tight junction formation in cultured pigment epithelial cells.

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Abstract

PURPOSE: These experiments were designed to characterize tight junction formation by retinal pigment epithelial (RPE) cells in vitro and to compare the effects on this process of hormonally defined medium (HDM) and serum-containing medium. METHODS: Formation of RPE tight junctions was analyzed in freshly isolated rat RPE cells maintained either in HDM or serum-containing medium. Junctions were evaluated functionally by measuring transepithelial electrical resistance (TER) and permeability and structurally by immunolocalization of the junction-associated actin microfilaments. Calcium dependency of the junctions was determined by reducing media calcium concentration. RESULTS: RPE cells cultured in serum-free HDM developed calcium-dependent tight junctions, which exhibited TER levels > 150 omega cm2 and low paracellular permeability. Serum-containing media inhibited tight junction formation as indicated by significant reductions in TER and increases in permeability. Junction-associated actin microfilaments and cell density were unchanged. CONCLUSIONS: Tight junction formation by RPE cells is inhibited by serum. This activity may play an important role in responses of the RPE layer to injury, contributing to the pathologic progression of blood-retinal barrier dysfunction.