Enhancement of urate solubility by connective tissue. II. Inhibition of sodium urate crystallisation by cation exchange.

The urate concentration of the supernatant was greater after supersaturated solutions of sodium urate were incubated in a suspension of CM-Sephadex C-25 than in one of Sephadex G-25. The supernatant urate concentration was greater when the CM-Sephadex had been equilibrated with potassium than with sodium. The results are analogous with those obtained in studies of urate solubility in proteoglycan solutions. They are consistent with the Donnan effect and the hypothesis that the glycosaminoglycans within the proteoglycan molecule function as cation exchangers which, when charged with potassium, exchange with the sodium of the urate molecule, leading to formation of highly soluble potassium urate.