Binding of the chromium-ethylenediaminetetraacetic acid complex (CrEDTA) to human albumin

The renal plasma clearance of the 51Chromium labelled complex with ethylenediaminetetraacetic acid ([51Cr]EDTA) underestimates that of inulin by 5-15%. Interaction of the anionic CrEDTA with polyanions in the glomerular filter and tubular reabsorption may add to the difference. A re-examination of the protein binding of CrEDTA showed that the protein binding is not negligible, because following ultrafiltration in vitro, the molality of CrEDTA was 5% lower in the ultrafiltrates than in the retentates. With a correction for the distribution of small ions this indicates at least 10% binding to human albumin. pKA = 7.36 was found for the equilibrium CrEDTA(H2O)- in equilibrium with CrEDTA(OH)2- + H+. One CrEDTA molecule carries one or two negative charges at near physiological pH. Renal plasma clearance of [51Cr]EDTA may be corrected to glomerular filtration rate (GFR) by multiplication with 1.10.