Purchase this article with an account.
J. W. Huff, Z. Hogan, A. Ishola, J. Dortch; Effects of Divalent Cations on Bovine Corneal Stromal Swelling Rates. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3507.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The corneal stroma swells with edema fluid largely due to electrostatic repulsion between its anionic glycosaminoglycans (GAGs), but swelling is slower in solutions of divalent cationic (alkaline earth metal) salts. To determine why, we compared hydration rates of stromas bathed in phosphate buffered saline (PBS) vs solutions of divalent metal and non-metal (diamine) salts to determine if charge:mass ratio, ionic strength or coordination bonding (to outer shell electrons of nitrogen and oxygen of GAGs) is a requirement for inhibition of stromal swelling. Unlike divalent metals, diamines do not coordination bind to the oxygens or amines of GAGs.
Fresh cattle eyes were obtained in zip-lock bags placed on ice from a local abattoir and transported to the laboratory. Corneas were removed and separated from the iris, lens and ciliary body and punched to 20 mm diameters with a leather punch. Their epithelia were removed by scraping with a #22 scalpel blade and their endothelia were removed with an unbleached paper towel. We refrigerated stromas in moist chambers overnight and in 180 minute experiments, measured stromal wet mass vs time in phosphate buffered 148 mM saline (PBS) or 4.8 - 148 mM sodium sulfate, magnesium sulfate, calcium chloride, hexamethonium dichloride, putrescine dihydrochloride and ethylenediamine hydrochloride substituted solutions. Dry mass was achieved in a 80° drying oven overnight. Hydration was calculated as (wet mass - dry mass)/(dry mass), i.e., (water mass)/(dry mass). Hydrations were compared at identical time points using a pooled Student’s t-test.
Hydration rate was fastest and (identical) in PBS and buffered 148 mM disodium sulfate, and slower in divalent cation salt solutions (p < 0.05). Both metal and nonmetal divalent cations decreased swelling rates in an equimolar, concentration-dependent fashion, regardless of molecular weight or chain length of the divalent cation. Graphically, hydration rates of stromas bathed in ethylenediamine, which is not divalent at pH 7.4, were superimposable on PBS controls. The effect was dependent on the concentration of the divalent cation and independent of the concentration of the anion (148 mM calcium chloride was equivalent to 148 mM magnesium sulfate).
Because all of the divalent cationic salts had the same efficacy to inhibit swelling rates, neither charge:mass ratio, metal coordination bonding, simple osmotic strength nor chemical normality appears to play a role in the divalent metal salts’ effects. All the divalent cations appear to equally decrease swelling, regardless of size, by shielding repulsive negative charges between GAGs.
This PDF is available to Subscribers Only