Anion binding in bovine corneal stroma

Abstract

Purpose: The corneal stroma strives to take up water because of the osmotic gradient created by fixed negative charges within the stroma. This fixed negative charge is known to be partly due to glycosaminoglycans and thought to be partly due to bound Cl− ions in the stroma. This study investigates the presence of anion binding within bovine stroma.Methods: Bovine corneas were isolated, de‐epithelialized and de‐endothelialized. The stromal uptake of NaCl, NaAcetate, NaThiocyanate and NaHCO3 solutions at various concentrations was observed using a digital balance. The dry weight of each cornea was noted. Stromal hydrations were calculated and analysed.Results: As the bathing solution concentration increased, for all solutions there was a significant increase in the calculated fixed negative charge values obtained. At physiological concentration of NaCl (150 mM), the fixed negative charge was calculated to be 39.98 ± 1.05 mEq 1−1. For NaAcetate, NaThiocyanate and NaHCO3 at 150 mM the fixed negative charge was calculated to be 38.64 ± 0.51, 43.62 ± 0.51 and 41.98 ± 0.65 mEq 1−1 respectively (n = 10, ± SEM).Conclusions: The degree of anion binding in bovine corneal stroma varies from anion to anion and is dependent on the external bathing solution concentration. At 150 mM, the binding series from this study is NaThiocyanate > NaHCO3 > NaCl > NaAcetate.