Chloride binding in the stroma of cultured human corneas

In the ox cornea, more than half of the non-diffusible, matrix negative charge is derived from the binding of free chloride ions. Because the magnitude of the net matrix charge is the dominant factor which determines the degree of stromal swelling, we investigated whether this phenomenon, stromal chloride binding, also occurs in human corneal stroma. Intrastromal ion concentrations were measured with radio-isotopes when human (outdated Eye Bank) corneas or (fresh) bovine corneas, physically clamped to maintain a constant hydration, were incubated in buffered 154 mM NaCl. The intrastromal chloride ion concentration was compared to the normalized concentrations of trace quantities of radio-labelled acetate and lactate ions. For human corneas, the intrastromal chloride ion concentration was found to be significantly higher (P < 0.001, t-test) than the normalized concentrations of both acetate and lactate ([Cl]i = 142.5 +/- 0.9 mM, (n = 9); [acetate]i = 131.2 +/- 1.2 mM, (n = 8); [lactate]i = 131.9 +/- 1.5 mM, (n = 5); all values are mean +/- S.E.M.). The sodium ion concentration was elevated ([Na]i = 176.0 +/- 1.8 mM, (n = 9)). These results demonstrate that chloride binding occurs to a significant extent in cultured human corneal stroma and suggest that chloride binding may be evident in the native human cornea.