Conditioned medium from mixed retinal pigmented epithelium and Muller cell cultures reduces in vitro permeability of retinal vascular endothelial cells

Aim: To investigate the in vitro effect of laser photocoagulation on blood-retinal barrier permeability. Methods: Retinal capillary endothelial cells were exposed to supernatants from long term co-cultured cells that were argon laser treated. Endothelial cell permeability was analysed by (1) measurement of transendothelial electrical resistance and (2) equilibration of [H-3] inulin and [C-14] albumin across the cell monolayer. Results: Laser photocoagulation of various retinal cells and control ECV304 cells in the lower chamber did not appreciably improve permeability of the endothelial cell monolayer compared with that of unlasered cells. However, medium that was conditioned by mixed retinal pigmented epithelium and Muller cells significantly reduced both inulin (43.2% (SD 6.5%) equilibration in mixed cultures v 59.8% (SD 7.0%) control cells, p < 0.05) and albumin (15.1% (SD 3.8%) v 31.1% (SD 6.7%), p < 0.05) permeability of the endothelial cell monolayers. A fourfold increase in transendothelial electrical resistance was also seen. Conclusions: These results are consistent with the hypothesis that interaction of Muller cells with retinal pigmented epithelium induced by laser treatment results in secretion of soluble factor(s), which reduces permeability of retinal vascular endothelium. Identification of these factor(s) may have implications for the clinical treatment of macular oedema secondary to diabetic retinopathy and other diseases.