SERUM INHIBITS TIGHT JUNCTION FORMATION IN CULTURED PIGMENT EPITHELIAL-CELLS

Purpose. These experiments were designed to characterize tight junctio n 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 junction s 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 permeabil ity and structurally by immunolocalization of the junction-associated actin microfilaments. Calcium dependency of the junctions was determin ed by reducing media calcium concentration. Results. RPE cells culture d in serum-free HDM developed calcium-dependent tight junctions, which exhibited TER levels > 150 Omega.cm(2) and low paracellular permeabil ity. Serum-containing media inhibited tight junction formation as indi cated by significant reductions in TER and increases in permeability. Junction-associated actin microfilaments and cell density were unchang ed. Conclusions. Tight junction formation by RPE cells is inhibited by serum. This activity may play an important role in responses of the R PE layer to injury, contributing to the pathologic progression of bloo d-retinal barrier dysfunction.