SIMULTANEOUS MEASUREMENTS OF CALCIUM-OXALATE CRYSTAL NUCLEATION AND AGGREGATION - IMPACT OF VARIOUS MODIFIERS

Rates of nucleation and aggregation of calcium oxalate crystals were d erived from 20-min time course measurements of OD620 after mixing solu tions containing CaCl2 and K2C2O4 at 37 degrees C, pH 5.7, ionic stren gth (IS) 0.21, with constant stirring (500 rpm); final assay concentra tions were 4.25 mM calcium and 0.5 mM oxalate, respectively. The maxim um increase of OD620 with time, termed S-N, mainly reflects maximum ra te of formation of new particles and thus crystal nucleation. After eq uilibrium has been reached, OD620 progressively decreases despite ioni zed calcium staying constant and no new particles being formed, due to crystal aggregation. Rate of aggregation, S-A, is derived from the ma ximum decrease in OD620 with time. S-N and S-A are not independent, as indicated by a positive correlation (r = 0.844, P = 0.0001). Among th e modifiers studied, citrate at 0.5-2.5 mM lowered both S-N and S-A in a concentration-dependent manner (P < 0.01 for all comparisons vs con trol). Chondroitin-6-sulfate at 6.25-25 mg/l moderately lowered S-N, w hereas it strongly inhibited aggregation (P<0.01 vs control). At 6.8-2 0.4 mg/l, albumin did not affect nucleation, whereas it inhibited aggr egation in a concentration-dependent manner (P < 0.005 vs control for all comparisons).