Photodynamic alteration of cornea endothelium. Relation to bicarbonate fluxes and oxygen concentration.

Corneas were mounted in flux chambers and endothelial bicarbonate fluxes were determined following sensitization of endothelial cells with 5 . 10(-6) M rose bengal and exposure to light. Corneas exposed to light demonstrated an increased passive bicarbonate flux compared to corneas not photosensitized. Active bicarbonate flux was reduced after 5 min of light exposure, but not after 1 min of light exposure. The increase in passive bicarbonate flux was prevented by the addition of 200 microgram/ml catalase to the bathing solution; however, catalase had no effect on the photodynamic alteration of active flux. Neither 10 mM ascorbic acid nor 1.012 gram/l glutathione prevented the photodynamically induced increase in passive flux. Perfusion of corneas with 5 . 10(-6) M rose bengal dissolved in a sucrose-substituted Krebs-Ringer bicarbonate solution with a PO2 of 124 +/- 4.0 mmHg and exposed to light swelled at rates more rapid than corneas treated in a similar fashion but perfused with a solution with a PO2 of 20 +/- 4.6 mmHg. This study demonstrated that photodynamically induced corneal endothelial cell alteration results in increased passive bicarbonate flux, a time-dependent decrease in active bicarbonate flux, is oxygen dependent, and is at least in part secondary to H2O2 produced by the dismutation reaction of the superoxide free radical.