Visualization of ouabain binding in bovine cornea

Extracellular matrix and Na+,K+-ATPase in human corneas following cataract surgery: comparison with bullous keratopathy and Fuchs' dystrophy corneas

PURPOSE

To examine the distribution of extracellular matrix (ECM) and basement membrane (BM) components and of Na+,K+-ATPase in postcataract surgery (PCS) corneas. These corneas were from patients who never developed pseudophakic or aphakic bullous keratopathy (PBK/ABK) after cataract surgery. PCS corneas were compared with PBK/ABK and Fuchs' dystrophy corneas.

METHODS

The distribution of PBKIABK ECM and BM markers and of all three Na+,K+-ATPase alpha subunits was studied by immunofluorescence in 10 healthy, 11 PCS, 16 PBK/ABK, and 12 Fuchs' dystrophy corneas.

RESULTS

Fibrotic ECM proteins, tenascin-C and fibrillin-1, were found in only 1 of 10 healthy and in 2 of 11 PCS corneas. In contrast, these proteins were expressed in all PBK/ABK and more than half of the Fuchs' dystrophy corneas. BM components in PCS corneas were altered to a greater extent (40-60%), especially fibronectin and laminin-10. A decreased epithelial immunostaining for Na+,K+-ATPase alpha subunits was seen in approximately 40% of PCS corneas and in approximately two thirds of PBK/ABK and Fuchs' dystrophy corneas. However, the endothelial staining was normal in all groups.

CONCLUSIONS

Because tenascin-C and fibrillin-1 were mostly found in diseased but not in PCS corneas, their expression may be related to later, clinical stages of corneal edema development. However, BM components abnormal in PBK/ABK and Fuchs' dystrophy corneas were also altered in PCS corneas without clinical evidence of ocular disease. This may result from subclinical corneal changes resulting from cataract surgery, lens removal, exposure to the intraocular lens, or endothelial cell damage. Alterations of epithelial Na+,K+-ATPase point to the importance of epithelial changes in the development of corneal edematous diseases.

Toxic effects of ouabain on the rabbit corneal endothelium

Rabbit corneas kept in a standard tissue culture medium, were continually exposed to ouabain 10(-3) M, and cultivated for 2, 3 and 4 days. The endothelium was still intact with a complete cell cover after 2 days of ouabain exposure. Total destruction of the endothelium was found in the corneas cultivated for 3 and 4 days. The corneal epithelium, however, appeared to be unaffected. Other rabbit corneas were exposed for three days to ouabain concentrations of 10(-4) M, 10(-5) M, 10(-6) M, 10(-7) M, 10(-8) M, and 0 M. The corneas exposed to 10(-4) M demonstrated total endothelial cell damage. The specimens exposed to concentrations from 10(-5) to 10(-8) M, presented dose dependent endothelial impairment as compared with the control corneas (0 M). Tracer experiments showed that the endothelial barrier was intact as long as there was a continuous cell cover, as estimated by light, transmission and scanning electron microscopy.