Uptake and processing of human platelet factor 4 by hepatocytes.
We previously demonstrated rapid clearance of human platelet factor 4 (PF4) from rabbit and rat blood, its accumulation in the liver, and elimination of PF4 degradation products in urine. The purpose of the present experiments was to characterize interaction of PF4 with cultured rat hepatocytes. 125I-PF4 was taken up by hepatocytes reaching maximum at 180 min. The association of 125I-PF4 with hepatocytes was two times greater at 37 degrees C than at 4 degrees C. At 37 degrees C degradation of 125I-PF4 by hepatocytes was also observed as indicated by the increase of 125I-PF4 radioactivity soluble in 6% trichloroacetic acid. By contrast, no uptake of 125I-beta-thromboglobulin antigen was observed. Autoradiography demonstrated that short incubation (5-20 min) of 125I-PF4 with hepatocytes results in the association of 125I-radioactivity with cell membranes while after longer incubation (60 min) radioactivity was also localized in the endosomes. Heparin inhibited binding and uptake of 125I-PF4 radioactivity by hepatocytes. We propose that part of PF4 released in the circulating blood by activated platelets is bound to the surface of hepatocytes and that it is further processed by these cells.
Department of Physiology and Medicine, Temple University School of Medicine, Philadelphia, PA 19140.
B
B
Rucinski
G J
GJ
Stewart
P A
PA
De Feo
G
G
Boden
S
S
Niewiarowski
D000818:Animals; D001345:Autoradiography; D006801:Humans; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008854:Microscopy, Electron; D010978:Platelet Factor 4 / Q000493:pharmacokinetics*; D051381:Rats
D010978:Platelet Factor 4