Uptake and Flow-induced Release of Uridine Nucleotides from Isolated Vascular Endothelial Cells

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Abstract
Endothelial cells were isolated from rabbit thoracic aorta and cultured. Uptake of radioactivity was studied during incubation with 3H-uridine and 3H-uridine triphosphate (3H-UTP). After incubation with 3H-uridine and analysis by thin layer chromatography, the pyrimidines detected in the cell cytoplasm were 3H-UTP (30.8 ± 0.9%), 3H-UDP (uridine diphosphate, 4.3 • 2.1%). 3H-UMP (uridine monophosphate, 53.6 ± 1.1%) and 3H-uridine (7.1 3 0.9%). After incubation with H-UTP, there was also an uptake of radioactivity which was inhibited at low temperature (89.9 ± 6.1% at 4 °C), by dipyridamole (89.0 ± 7.1%) and N-ethylmaleimide (79.2 • 4.3%). The pyrimidines detected were 3H-UTP (24.7 • 3%), 3H-UDP (4.6 ± l%), 3H-UMP (35 ± 3.7%) and 3H-uridine (18.4 • 5%). Cultured endothelial cells were incubated with 3H-UTP or 3H-uridine and 3H-uridine for 90 min. These cells were perfused (0.5 ml/min) then stimulated twice by increased flow (3.0 ml/min) in order to compare their ability to release UTP and its derivatives. UTP and its metabolites were released during perfusion. The release was significantly higher during periods of increased flow (4 × for the first period; 2 × for the second). The pyrimidines detected in the perfusate, during periods of increased flow, were 3H-UTP, 3H-UDP, 3H-UMP and 3H-uridine. To conclude, this study shows that vascular endothelial cells take up uridine, and that UTP, UDP, UMP and uridine are released upon stimulation of the cells by increased flow.

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