Kinetic evidence of a surface membraneous step during the endocytosic process of 3H-labelled asialoorosomucoid and its alteration in diabetic mellitus rats.

The apparent internalization rate constant of asialoorosomucoid in normal and diabetic hepatocytes was determined using different experimental processes, either following a synchronous wave of prebound ligand or a continuous flux ligand endocytosis, either alone or simultaneously. In continuous flux conditions, no difference between normal and diabetic hepatocytes appeared (k = 0.15 +/- 0.04 and 0.11 +/- 0.02 min-1, respectively). In contrast, in the one-turn endocytosis of prebound ligand, k was lower for diabetic hepatocytes than for normal ones whether it was measured alone (0.20 +/- 0.03 and 0.59 +/- 0.09 min-1, respectively) or simultaneously with a continuous flux of unlabelled ligand (0.25 +/- 0.03 and 0.70 +/- 0.08 min-1, respectively). These differences are attributed to an impediment or a delay in the preclustering of receptors in coated pits at the cell surface of diabetic cells.