Binding of Bilirubin to Erythrocytes 1

Abstract

Summary

Bovine erythrocytes were incubated in buffered media (pH 7.4) containing ¹⁴C-bilirubin and bovine serum albumin in molar ratios from 0.04 to 1.5. After equilibration, erythrocytes and media were separated by centrifugation and the level of ¹⁴C-bilirubin in media was determined. Bilirubin binding to erythrocytes was then correlated with the proportion of nonalbumin-bound bilirubin in media, determined ultracentrifugally.

At a given albumin concentration, erythrocytes and albumin bound constant proportions of bilirubin, despite varying bilirubin concentrations. Upon changing albumin concentrations, a linear relationship was found between extents of bilirubin binding to erythrocytes and to albumin, whereby an increase of only 3% in nonalbumin-bound bilirubin resulted in 5-fold increased bilirubin binding to erythrocytes.

Adding salicylate did not influence bilirubin binding to erythrocytes other than was predictable from increased unbinding of albumin-bilirubin complex.

In evaluating functioning of the liver from observed rates at which an administered compound is cleared from serum, the extent of binding to erythrocytes must be considered. It would appear that such binding can be estimated arithmetically when the proportion of nonalbumin-bound compound has been measured.