Phorbol ester modulation of rabbit corneal endothelial permeability

Purpose. Phorbol esters have been shown to have a profound influence on cellular activity in many cell types. The purpose of this study was to examine the influence of phorbol esters on the function and structure of corneal endothelial cells. Methods. Corneas were placed under a specular microscope, and the endothelium was super-fused with glutathione bicarbonate Ringer's solution (GBR); with GBR and 10 nM. 100 nM, or 1 μM 4β-phorbol 12- myristate 13-acetate (PMA); or with 100 nM 4-α-PMA. Corneal swelling curves were generated, and endothelial permeability was determined. Corneal endothelial structure was examined with a scanning electron microscope. Results. Significant increases in swelling and endothelial permeability were found in corneas perfused with 100 nM PMA versus that observed in controls (swelling rate: 26 μm/hr versus 6.9 μm/hr; permeability = 6 x 10^-4 cm/min versus 3.4 x 10^-4 cm/min) and in corneas receiving 1 μM PMA versus that in controls (swelling rate = 26.3 μm/hr versus 0.12 μm/hr; permeability = 6.9 x 10^-4 cm/min versus 4.9 x 10^-4 cm/min). Application of 10 nM PMA did not significantly alter either parameter. Study with transmission electron microscope demonstrated significant morphologic changes in cells perfused with all concentrations of PMA. Corneas perfused with 100 nM 4-α-PMA versus 100 nM PMA had significantly lower slope and permeability values (swelling rate = 5.9 μm/hr versus 25.1 μm/hr; permeability = 3 x 10^-4 cm/min versus 6.7 x 10^-4 cm/min). Conclusions. Phorbol esters are detrimental for corneal endothelial function, creating significant corneal swelling, increases in endothelial permeability, and changes in endothelial cell structure. This effect appears to be mediated through a protein kinase C pathway.