Toxic effects of copper on cultured rat lenses

The pathophysiology of the ocular microenvironment. II. Copper-induced ocular inflammation and hypotony

The ocular effects of intravitreally injected copper sulfate solutions were studied in New Zealand white rabbits. These injections resulted in uveitis characterized by prolonged ocular hypotony, increased protein concentrations and decreased ascorbic acid concentrations in both the vitreous and aqueous humors, and an apparent decrease in the transport function of the anterior uvea. The extent and the duration of these effects were dose-dependent. The lower doses used, 3 or 6 micrograms of Cu as CuSO4 per eye, produced reversible inflammation. The highest dose, 30 micrograms of Cu per eye, also produced some signs of ocular chalcosis: hemorrhage, vitreous liquefaction, prolonged hypotony and local iridial ischemia. Six hours after the intravitreal injection of 6 micrograms of Cu as CuSO4 per eye, the Cu concentration in the vitreous humor increased to approximately 100 times that in the vitreous of control eyes, and began to decline only 3 days later, with a half-time of approximately 8 days. The Cu concentration in the anterior chamber of these eyes never exceeded 1 ppm and returned close to control values within 3 days. Based on these findings, factors that affect ocular trace-metal distribution and kinetics are discussed, as are reasons for the apparent difficulty in diagnosing the presence of Cu-containing intraocular foreign bodies on the basis of the Cu concentration of the aqueous humor.

Copper exchanges and toxicity in the rabbit lens in vitro

Lenses (in vitro) exposed to 10(-4) M Cu for 24 hr gained an excess of Na and lost K. Incubation for 7 days with 10(-5) M Cu had a similar toxic effect. Threonine, which is present in aqueous humor, increased sensitivity of lenses to Cu, and also uptake of 64Cu. Uptake of 64Cu commenced reaching tissue saturation levels in 5 hr at 10(-7) M Cu. At higher concentrations, uptake was greater (1263 X for a 1000-fold rise in concentration from 10(-7) -10(-4) M) and saturation was not seen in this time. Autoradiography of sections of such lenses suggested that accumulation of the 64Cu occurred principally within the region of the cells of the anterior epithelium and capsule and lens bow. Efflux of accumulated 64Cu occurred more rapidly when copper was present in the external media suggesting the presence of 'specific' binding sites for copper. Percentage retention of accumulated 64Cu was greater in lenses loaded in 10(-6) M than 10(-5) M Cu. It is suggested that copper can enter lenses, possibly facilitated by threonine, and can bind to two types of sites: one with a high affinity but low capacity for the metal ion, the other with a lower affinity but larger capacity. The former may be concerned with the physiological roles and normal metabolism of copper and the latter with its toxic actions.

The role of divalent cations in controlling amphibian lens membrane permeability; the mechanisms of toxic cataracts

The effects of a range of divalent ions on lens sodium and potassium permeability characteristics were studied in calcium competition and replacement experiments. Resting voltage and conductance were measured and also voltage-independent conductance. Strontium and manganese were the only divalent ions able to maintain, in the absence of calcium, both sodium and potassium permeability at or near the control level. Neither cobalt nor magnesium had any effect on lens voltage of conductance in the presence of calcium, but neither of these ions could maintain lens permeability properties in the absence of calcium. Cadmium and barium had little effect on sodium permeability, but the former increased potassium permeability while the latter reduced it. Barium was the only divalent studied that appeared to inactivate voltage-sensitive potassium channels in the presence of calcium. Nickel, zinc and copper increased both sodium and potassium permeability in the presence of calcium and so they are likely to be particularly damaging to the lens. Copper was extremely toxic since it was able to overturn the regulatory influence of calcium when it was present in concentrations as low as 10(-6)M.