Influence of ionic strength on crystal adsorption and inhibitory activity of macromolecules

We investigated the influence of ionic strength on both the binding ability of macromolecules onto calcium oxalate crystals and the inhibitory activity of macromolecules related to calcium oxalate crystal growth and aggregation in vitro. The amount of heparin sodium salt adsorbed onto calcium oxalate crystals was studied in both a seed and a non-seed crystal system at various ionic strengths with the aid of radiolabelled heparin. In both adsorption models, adsorption of heparin was greater in the buffered solutions of lower ionic strength, and significantly so in the range of physiological ionic strength. The inhibitory activity of heparin in the non-seed crystal system, which was determined using a Coulter Multisizer, increased as the adsorbed dose increased. The naturally existing urinary macromolecules showed a similar change in their inhibitory activity on calcium oxalate crystal growth and/or aggregation in accordance with changes in ionic strength. These results indicate that macromolecular inhibitory activity seems to be enhanced in urine of lower ionic strength as a result of an increased adsorption of macromolecules on the surface of calcium oxalate crystals.