Abstract
The corneal swelling rate, endothelial passive permeability for sucrose, and endothelial fine structure were studied in a series of paired rabbit corneas in which one member was allowed to swell in a Ca++-free medium to a prescribed thickness before permeability measurement and subsequent fixation, and the other member returned to a complete medium to determine the reversibility of the corneal swelling, passive permeability increase, and changes in endothelial fine structure caused by the Ca++-free perfusion. Both physiologic and morphologic manifestations of the breakdown of the endothelial permeability barrier increase with time of perfusion with a Ca++-free medium, but both are reversible if a cornea is returned to a complete medium before it has reached 150 per cent of normal thickness. Between 150 and 200 per cent of normal thickness the effects of Ca++-free perfusion may be attenuated but not reversed; over 200 per cent no change in the slope of the swelling curve was found, and the passive permeability for sucrose was so high as to be effectively immeasurable. Corneas reversed in the presence of 45Ca had autoradiographically demonstrable isotope localization in the endothelial functional zone. Microfilament assemblies normally seen near the junctional complex in the apical endothelial cytoplasm are disrupted in the Ca++-free state but again appear normal after the reversal of the Ca++-free swelling and reestablishment of the normal passive permeability coefficient and normal junctional morphology