The permeability in vitro bf rabbit corneal epithelium alone and whole cornea to four radioactivesubstances of various molecular weights-tritiated water (THO: molecular weight 22), mannitol (molecular weight 182), inulin(molecular weight 5, 175), and dextran (molecular weight 77,500)-was directly measured by using a newly designed lucite chamber (Fig. 1) and a proportional counter system for radioisotope experiments.
The permeability of the corneal epithelium and the whole cornea varied with the size of molecular weight (Fig. 4) and curvilineally with respect to molecular radius (Fig. 5).
Certainly the data (Table 2 and 3) support that the greater part of non-electrolyte permeation was through intercellular spaces passively.
The epithelial or whole corneal permeability fell markedly as the molecular weight increased from 22 to 5,175. Above the molecular size of inulin, the permeability decreased much as the molecular weight increased.
Generally, tritiated water permeability was about 150 times greater than that of mannitol and about 2, 000 times than that of inulin and about 10, 000 times than that of dextran.
The difference between the permeability of the epithelium alone and that of the whole cornea was not noticed.
Futhermore, the permeability, either of epithelium alone or the whole cornea, did not vary significantly depending upon the location of the hot side with any of the four kinds of isotope-labelled solutes, whether it was set at the epithelial or endothelial side of the corneal membrane (PCO.1).
These results may support that the epithelial layer plays a main role as a physical barrier for nonelectrolyte solutes movement across the rabbit cornea.
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