Swelling studies of bovine corneal stroma without bounding membranes.

Abstract

SUMMARY1. The swelling characteristics of demembranated bovine corneal stroma were studied as a function of time and of the pH and ionic strength of the bathing solution.2. Compared with other pH values, the stroma swelled least near pH 4. 3. In the pH range 6-10, increasing the pH resulted in an increase both in the rate of swelling and in the hydration reached in a given time.4. At pH 2 and 4, a final constant value of hydration was attained. At higher pH values no such equilibrium was attained when the hydration of the tissue was followed for at least 100 hr.5. The swelling at high pH values was consistent with the hypothesis that the Donnan-osmotic contribution is the major component of the swelling pressure.6. The ionic strength dependence was complex. There was a general decrease of swelling with increase in the ionic strength (iu) until around /t = 0-1. The swelling at u=0-15 was greater than at /= 0-1 and 1z = 0-25. 7. The results were interpreted on the assumption that the Donnan-osmotic effect is the major component of the swelling pressure.

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

“…In cornea, a substantial part of the fixed net negative charge on the proteins arises from immobilized anions (probably largely chloride ions) trapped in potential wells or otherwise fixed to the protein surfaces (Elliott, 1980;Elliott et al 1980). 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.…”

The contribution of glycosaminoglycans to the mechanical behaviour of the posterior human sclera

“…The decrease in thickness in the human sclera after enzymetreatment could result from an overall loss of water with s-GAG degradation. The amount and type of negative ionic charges determine the scleral capacity for water absorption through charge [29] and osmotic [30][31][32] effects. However, the water absorption capacity of the tissue is also limited by the collagen interfibrillar spacing, itself governed by GAG-GAG charge repulsion [40] and GAG-GAG anti-parallel interactions [41].…”

The measurement of ox corneal swelling pressure by osmometry.

“…If a small correction for hydration is included (Elliott and his coworkers assumed a physiological hydration of 3 4, whereas we used our measured physiological hydration of 3 2) the correspondence of the independently determined values for the fixed stromal charge is even closer. It appears that Donnan theory predicts accurately intrastromal electrical potential (Elliott, 1980), free swelling rates of stroma in saline (Elliott, Goodfellow & Woolgar, 1980) and corneal gel pressure measured by osmometry (current study) over a wide range of corneal hydrations. The theory accounts quantitatively for all the observed properties of corneal swelling except for one important group of exceptions, which all concern the measurement of corneal swelling pressure by mechanical methods.…”

“…1) then weight equilibrium was not attained, and even though the preparation might show an initial tendency to deturgesce, eventually tissue weight gain was progressive. In the whole-corneal preparations, where equilibrium was attained, the natural tendency of cornea to swell in saline (Elliott, Goodfellow & Woolgar, 1980) is balanced by the osmotic pressure generated by the non-penetrating solute (PEG 1OK) in the bathing solution.…”

“…The other criticism levelled at Donnan theory is that corneas immersed in hypertonic saline swell more rapidly than predicted by Donnan theory. The explanation given by Elliott et al (1980) is that the matrix charge is composed not only of the sulphonic and carboxylic acid groups of the matrix glycosaminoglycans but also of chloride ion binding to the stromal matrix which increases stromal negative charge and which may explain the relatively high swelling rates in high salt. We propose to investigate these possibilities further.…”