Effects of divalent cations on bovine corneal stromal swelling rates

Purpose: The corneal stroma swells with edema fluid due to electrostatic repulsion of its negatively charged glycosaminoglycans, and divalent metal cations inhibit edema development. We investigated whether or not nonmetal divalent cations might also inhibit edema development. Materials and Methods: We investigated the hydration rates of stromas bathed in phosphate-buffered saline (PBS) or phosphate-buffered magnesium sulfate, calcium chloride, hexamethonium dihydrochloride, putrescine dihydrochloride, and ethylenediamine hydrochloride solutions at pH 7.35-7.4. Results: Hydration rate was fastest in PBS and slower in divalent cation salt solutions (p < 0.05). All metal and nonmetal divalent cations inhibited swelling rates compared to PBS. Ethylenediamine is not divalent at physiological pH and did not significantly inhibit swelling. Conclusions: All the divalent cations appear to decrease swelling relatively equally, probably by shielding negative charges on GAGs, reducing their electrostatic repulsions.