Transient chloride binding as a contributory factor to corneal stromal swelling in the ox.

Abstract

SUMMARY1. Investigations were made of the cation exchange capacity of fresh isolated ox corneal stroma (Q, units: mequiv fixed stromal charge/kg stromal fluid) at pH 7f4 over a variety of stomal hydrations (H, units: kg stromal fluid/kg dry tissue) both above and below the physiological hydration of 3-2, whilst the stromas were immersed in a variety of sodium chloride solutions (range 5-1000 mM).2. At any particular salt concentration, the product QH (dry tissue exchange capacity, units: mequiv/kg dry tissue) appeared constant, over all the hydrations investigated.3. Dry tissue exchange capacity (QH) varied, however, when the bathing salt concentration was altered. It varied between 55 mequiv/kg dry tissue (e.g. Q = 17 mequiv at H = 3-2) in 5 mM-NaCl to 240 mequiv/kg dry tissue (e.g. Q = 75 mequiv/l at H = 3'2) in 1000 mM-NaCl.4. The variation of stromal exchange capacity in NaCl solutions of different concentrations was similar when detected by three independent procedures: stromal gel pressure measurements, intrastromal sodium ion distributions, and intrastromal electrical potentials.5. Intrastromal chloride ion distributions were anomalous. Total chloride (measured by radio-isotopes) was consistently higher than that predicted by Donnan theory.6. The data were consistent with Elliott's hypothesis that a fraction of intrastromal chloride ions bind to the corneal stromal matrix and in so doing contribute to the fixed negative charge of the stroma.7. Our observations may be explained by a model of the cation exchange capacity of ox cornea which has two types of components. On is (at constant pH) invariant, and has a dry tissue exchange capacity of about 50 mequiv/kg dry tissue, and is probably generated by the sulphonic and carboxylic acid groups of the glycosaminoglyeans. The other is explained by supposing it to consist of a chloride binding ligand which exhibits first order binding, is half occupied at ambient chloride concentrations of 300 mm, and has a total capacity of 240 mequiv/kg dry tissue. 8. Partial stromal extraction with 4 M-guanidine HCl indicated that the chloride

Proceedings of the Physiological Society, 23‐25 September 1992, Cambridge Meeting: Communications

“…Hodson et al (1992) have confirmed that transient chloride binding is a large contributory factor to corneal stromal swelling in the ox in the physiological regime, showing that the model described here is reasonable. An increase in temperature will decrease the amount of anionic immobilization, by the operation of Boltzmann's theorem.…”

The Effect of Hydration and Matrix Composition on Solute Diffusion in Rabbit Sclera

“…It was shown that when the hydration is 41, the intermolecular spaces do not change substantially, in either cornea or sclera (Huang and Meek, 1999). In the cornea, Elliott, Goodfellow and Woolgar (1980) and Hodson et al (1992) suggested that about 50 % of the swelling tendency comes from the GAGs, and the rest from anion binding. It should be noted, however, that the putative ligand for chloride ions within the cornea has not yet been identi®ed.…”

Corneal collagen—its role in maintaining corneal shape and transparency

“…Swelling takes place only in one direction (through the corneal thickness). The driving force for this swelling is a Donnan osmotic force generated by the high negative charge on the proteoglycans and also by chloride binding to proteins (Hodson et al 1992). Maintenance of normal corneal thickness, and hence transparency, is provided in vivo by an outwardly directed electrogenic bicarbonate "pump" localised in the endothelial cells (Hodson and Miller 1976).…”