Thromb Haemost 1988; 59(03): 474-479
DOI: 10.1055/s-0038-1647518
Original Article
Schattauer GmbH Stuttgart

Uptake and Degradation of Tissue Plasminogen Activator in Rat Liver

Monica Einarsson
1   The Research Department Biochemistry, KabiVitrum AB, Stockholm, Sweden
,
Bård Smedsrød
2   The Department of Medical and Physiological Chemistry, University of Uppsala, Uppsala, Sweden
,
Håkan Pertoft
2   The Department of Medical and Physiological Chemistry, University of Uppsala, Uppsala, Sweden
› Institutsangaben
Weitere Informationen

Publikationsverlauf

Received 17. Juli 1987

Accepted after revision 19. Februar 1988

Publikationsdatum:
29. Juni 2018 (online)

Summary

The mechanism of uptake of tissue plasminogen activator (tPA) in rat liver was studied. Radio-iodinated tPA was removed from the circulation after intravenous administration in a biphasic mode. The initial half life, t1/2(α), and the terminal phase, t1/2(β), were determined to be 0.5 min and 7.5 min, resp. Separation of the liver cells by collagenase perfusion and density centrifugation, revealed that the uptake per cell was two to three times higher in the non-parenchymal cells than in the parenchymal cells.

Endocytosis of fluorescein isothiocyanate-labelled or 125I-labelled tPA was studied in pure cultures of liver cells in vitro. Liver endothelial cells and parenchymal cells took up and degraded tPA. Endocytosis was more efficient in liver endothelial cells than in parenchymal cells, and was almost absent in Kupffer cells.

Competitivb inhibition experiments showing that excess unlabelled tPA could compete with the uptake and degradation of 125I-tPA, suggested that liver endothelial cells and parenchymal cells interact with the activator in a specific manner. Endocytosis of trace amounts of 125I-tPA in cultures of liver endothelial cells and parenchymal cells was inhibited by 50% in the presence of 19 nM unlabelled tPA. Agents that interfere with one or several steps of the endocytic machinery inhibited uptake and degradation of 125I-tPA in both cell types.

These findings suggest that 1) liver endothelial cells and parenchymal cells are responsible for the rapid hepatic clearance of intravenously administered tPA; 2) the activator is taken up in these cells by specific endocytosis, and 3) endocytosed tPA is transported to the lysosomes where it is degraded.

 
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