Transferrin uptake by bone marrow macrophages is independent of the degree of iron saturation.
The uptake of transferrin by macrophages was studied in relation to the degree of iron saturation. Rat bone marrow derived macrophages were incubated with transferrin labelled with 59Fe and 3H. At 37 degrees C the amount of 59Fe incorporated by macrophages was dependent on the time of incubation. 3H labelled transferrin was found degraded in the supernatants of the cell culture (material not precipitated by trichloroacetic acid) in a time dependent fashion. Taking into account the specific activity of 59Fe-3H labelled transferrin, we found that 95% of the transferrin uptake was degraded. This suggests that most of the uptake of transferrin was not mediated by a receptor-dependent mechanism, but by a phase fluid endocytosis. 3H-labelled apotransferrin appears in the supernatant of the cell culture at the same rate as 59Fe-3H labelled diferric transferrin, showing an identical uptake for the two types of transferrin. Uptake of apo- or diferric transferrin by macrophages was identical in relation to time of incubation and the amount of transferrin used. These studies suggest that most of the transferrin uptake by bone marrow macrophages (non-activated or non-elicited cells) is mediated by a non-receptor mechanism that is independent of the degree of transferrin saturation.
Rama
R
R
Departamento de Bioquímica y Fisiología, Facultad de Biología, Universidad de Barcelona, Spain.
Sánchez
J
J
D000818:Animals; D001059:Apoproteins / Q000493:pharmacokinetics; D001853:Bone Marrow / Q000378:metabolism*; D002478:Cells, Cultured; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014168:Transferrin / Q000493:pharmacokinetics*
D001059:Apoproteins; D014168:Transferrin; C028284:apotransferrin; C028283:diferric transferrin; D007501:Iron