J. Biochem, 1988, Vol. 103, No. 2 348-353
© 1988 Japanese Biochemical Society
research-article |
The Cellular Dynamics of Hepatic Receptors for 
2-Macroglobulin.Protease Complex and for Insulin Are Different1
Institute of Physiology, University of Aarhus, Universitetsparken DK-8000 Aarhus C, Denmark
Making freshly isolated rat hepatocytes permeable by 0.4 g/liter digitonin doubled the number of binding sites for 
2-macroglobulin.trypsin complex without changing the affinity. Thus, digitonin unmasked a receptor pool, probably of intracellular origin. The total cellular binding capacity was measured in the presence of digitonin, the surface-exposed in its absence. Upon preincubation of the cells at 37°C, the total cellular binding capacity for 2-macroglobulin.trypsin decreased over a 2-h period to 0.26 of the initial value. By contrast, the surface-exposed binding capacity initially increased in response to a preincubation at 37°C, reached after 20 min a peak value 1.74 times that at 0 time, followed by a decrease. Neither the increase in nor the loss of surface-exposed binding capacity was influenced by inhibitors of lysosomal functions, protein synthesis and glycosylation. Colchicine abolished the increase in surface-exposed binding capacity but not the disappearance. By contrast, phenylarsine oxide (inhibitor of endocytosis), N-ethylmaleimide, and phenylmethanesulphonyl fluoride inhibited the receptor loss, suggesting that the loss occurred by proteolysis. The insulin receptor concentration, studied in parallel, remained practically constant in the investigated period in the presence and absence of digitonin. Thus, the hepatic receptor for 2-macroglobulin. protease complexes is regulated independently of other specialized plasma membrane proteins.
1This work was supported in part by grants from P. Carl Petersen's Fund (B-1545) and from The Danish Medical Association's Research Foundation (Højmosegaardlegatet).