CHLORIDE BINDING IN THE STROMA OF CULTURED HUMAN CORNEAS

In the ox cornea, more than half of the non-diffusible, matrix negativ e charge is derived from the binding of free chloride ions, Because th e magnitude of the net matrix charge is the dominant factor which dete rmines the degree of stromal swelling, we investigated whether this ph enomenon, stromal chloride binding, also occurs in human corneal strom a. Intrastromal ion concentrations were measured with radio-isotopes w hen human (outdated Eye Bank) corneas or (fresh) bovine corneas, physi cally clamped to maintain a constant hydration, were incubated in buff ered 154 mM NaCl. The intrastromal chloride ion concentration was comp ared to the normalized concentrations of trace quantities of radio-lab elled acetate and lactate ions. For human corneas, the intrastromal ch loride ion concentration was found to be significantly higher (P < 0.0 01, t-test) than the normalized concentrations of both acetate and lac tate {[Cl](i) = 142.5 +/- 0.9 mM, (n = 9); [acetate](i) = 131.2 +/- 1. 2 mM, (n = 8); [actate](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 strom a and suggest that chloride binding may be evident in the native human cornea. (C) 1995 Academic Press Limited