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SUMMARY Incubation of cultured porcine aortic and pulmonary endothelial cells and mediastinal fibroblasts in the presence of +-H-ATP resulted in the hydrolysis of the nucleotide and the appearance of adenosine, while, simultaneously, a saturable, temperature-dependent uptake of radioactivity was taking place. The same pattern was observed in the three cell types. Adenosine uptake was studied in the same cell populations and also found to be a saturable, temperature-dependent process. The presence of two components for the transport, a high affinity system (Km of 3 μ) and low affinity system (Km of 0.3-1.1 DIM), was established in both types of endothelial cells, as well as in fbroblasts (Km of 8.3 μM and 0.8 mivi). Endothelial cells, however, could be easily differentiated from fibroblasts on the basis of several kinetic features. In the three cell types, adenosine, once taken up, was rapidly phosphorylated under the action of adenosine kinase. No evidence of adenosine deaminase activity was found in intact cells, whereas conversion of adenosine to inosine was observed in a subcellular fraction of sonicated cells. The effect of low temperatures was more marked on adenosine kinase activity than on the uptake process itself. Inosine and adenine had no effect on the transport of adenosine, whereas dipyridamole, at 10∼6 M, had a very strong inhibitory action. The role of ATP and adenosine in the control of smooth muscle tone could be reexamined in view of their handling by endothelial cells of systemic and pulmonary origins.

Metabolism and uptake of adenosine triphosphate and adenosine by porcine aortic and pulmonary endothelial cells and fibroblasts in culture.