BINDING OF BILIRUBIN TO MAMMALIAN ERYTHROCYTES

Binding of bilirubin to erythrocytes of various mammalian species in t he presence of their respective plasma albumins was studied at pH 8.0, ionic strength 0.41 and at 37 degrees C. In human, buffalo, goat, and sheep, the amount of erythrocyte-bound bilirubin increased with the i ncrease in both the bilirubin/albumin molar ratio (B/A) and the total bilirubin concentration. In all species, the binding patterns were qua litatively similar. However, at any given B/A, goat erythrocytes bound the highest amount of bilirubin, followed by buffalo and human erythr ocytes; sheep erythrocytes bound the lowest amount of bilirubin. Incre ase in erythrocyte-bound bilirubin per unit increase in bilirubin conc entration at a constant BIA as obtained from the values of the slope o f the plot between erythrocyte bound bilirubin and total bilirubin in the incubate, was found to be highest for goat erythrocytes, followed by buffalo, human, and sheep erythrocytes. At a given bilirubin concen tration, percentage fractional binding of bilirubin between any two B/ As was found to be highest between 1.5 and 2.0, suggesting that a grea ter amount of bilirubin was transferred from plasma to cells between B /As 1.5 and 2.0. Percentage fractional binding of bilirubin was highes t in goat erythrocytes, followed by buffalo, human, and sheep erythroc ytes. These differences in the amount of erythrocyte-bound bilirubin w ere not due to the effect of various plasma albumins. These results su ggest that the difference in bilirubin binding by different mammalian erythrocytes can be attributed to the difference in either the affinit y of the erythrocyte receptors or their number or both. (C) 1997 Elsev ier Science Inc.