Elastic double system and selective permeability to cations in the stroma of the rabbit cornea.

Abstract

The attempt was made to cover the thermoelastic behavior and the selective permeability to ions of the cornea by taking into account the presence of negatively charged ionized groups fixed on the protein chains.The tension-temperature relations of the cornea were determined, and the entropic and energetic contributions to the net tension were calculated on the basis of the thermodynamic considerations.Over the range of moderate extensions, (1) positive tension is due entirely to the entropic contribution, (2) the internal energy makes a negative contribution to the tension.These results can best be explained by the superposition of two systems which oppose each other, i.e. an entropic system and the other in which electro-static repulsion between charged groups of like sign causes the tension.e long chain molcules bearing ionized groups of like sign can thus be envisaged as a sort of “elastic double system” the repulsion of these groups to stretch the chains, whereas the thermal motion of the segments tends compress them.Further evidence for the presence of ionized groups on the protein chains was provided by the experiments on the permeability to ions. The concentration chains with the chlorides of Na, K and Ca were measured; from the values of the P. D.'s the mobility ratios of the cations and anions within the stromaThe anion mobility is relatively more supressed within the stroma as com-pared with the cation, i.e. the stroma, is permeable selectively for cations. This could satisfactorily be explained by the negatively charged ionized groups of the protein molecules.Further, the fiber arrangement was studied in detail, and the radial fibers are, in the polarization optic sense, considered as dominant.The diagram is given showing a possible submicroscopic structure which can cover the known mechanical and optical characteristics and also the selec-tive permeability to ions.