Effect of bicarbonate on stability of the gallium-transferrin complex

When gallium citrate is injected intravenously the gallium is rapidly transchelated to transferrin. If the stability of the gallium-transferrin association is sufficiently strong it should be a good macromolecular tracer suitable for quantitative measurements of vascular permeability. Studies of the stability of the gallium transferrin complex in human plasma and serum were done using ultrafiltration and dialysis. It was found that the stability was sensitive to bicarbonate level. Above 13 mM of bicarbonate, 97%-99% of the gallium is bound to molecules greater than 10,000 MW by ultrafiltration. However, at 10 mM binding is 95% and at 7 mM 83%. Similar results were obtained with dialysis. This suggests the gallium-transferrin complex may not be sufficiently stable for quantitative measures of vascular permeability, particularly if the bicarbonate concentration is low.