Impairment of the phagocytic capacities of Kupffer cells, as is found in Frog Virus 3 hepatitis of mice, allows the endothelial liver cells to take up intravenously inoculated latex particles of 1.0 micron diameter. In vitro experiments with cultivated endothelial cells isolated by collagenase perfusion of the liver and purified by centrifugal elutriation demonstrate that uptake occurs via a typical mechanism of phagocytosis involving pseudopodia. Ingestion of latex is inhibited by incubation of the cells at 4 degrees C and by treatment with cytochalasin B, whereas colchicine has no effect. These results demonstrate that: the Kupffer cells are not the only cells of the hepatic sinusoid capable of phagocytosis; and under conditions where the phagocytosis in Kupffer cells is impaired, the endothelial cells may participate in the clearance of large particles from the blood.

SummaryThe relative contributions of the P2Y1 and P2YT receptors to the morphological changes induced in platelets by ADP or ADP-releasing agonists were assessed using two P2 antagonists, A2P5P and ARC67085, selective for P2Y1 and P2YT, respectively. The P2Y1 receptor was found to be involved in i) the centralization of secretory granules elicited by ADP, ii) the formation of filopodia induced by released ADP in weakly activated platelets and iii) actin polymerization and the cyto-skeletal translocation of cdc42, rac1 and rhoA, in an integrin IIb 3 dependent manner, in ADP-stimulated platelets. In contrast, the P2YT receptor was shown i) to be essential for the formation of stable macro-aggregates, ii) to enhance actin polymerization and the cytoskeletal translocation of small GTPases, probably through amplification of platelet aggregation, and iii) not to be involved in the early steps of platelet activation since its blockade did not affect the cytoskeletal translocation of rhoA.

Endothelial cells of the hepatic sinusoid isolated from mice livers and maintained in culture display typical fenestrae grouped in sieve plates. Treatment with cytochalasin B led to no significant change in the mean diameter of the fenestrae but to an increase in their number and in the porosity of the cells (percentage of the cellular surface opened by the fenestrae) which attained up to 300% of that of the controls. Scanning electron microscopic observations of Triton-extracted cells revealed that these modifications were related to an alteration of the cytoskeleton. The effect of cytochalasin B could be reversed; 3 hr after removal of the drug, the cells recovered their original aspect with sieve plates scattered over their surface. These observations demonstrate that endothelial fenestrae are inducible structures and that the cytoskeleton seems to be involved in their formation.

Human endothelial cells isolated from hepatic sinusoids were infected in vitro with human immunodeficiency