Depression of serotonin uptake by cultured endothelial cells exposed to high O2 tension

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Abstract
Serotonin (5-hydroxytryptamine, 5-HT), a vasoactive amine, is removed from the pulmonary circulation by active transcellular transport into endothelial cells, followed by intracellular metabolism. Pulmonary uptake of 5-HT is depressed by high partial pressures of O2 (PO2). To characterize the cellular basis and mechanism for hyperoxic depression of lung 5-HT uptake, the effect of high PO2 on 5-HT uptake by calf aortic endothelial cells in primary confluent monolayer was evaluated. Cells were exposed to either 95% O2 or 14% O2 (controls) in 5% CO2 at 1 atmosphere of absolute pressure for 20 or 42 h. Following exposure 5-[14C]HT (1 .times. 10-7 M) was added to the culture medium, and 5-HT uptake in pmol/106 cells was measured. Exposure to 95% O2 for 20 or 42 h resulted in significant depression of 5-HT uptake by cultured endothelial cells, and uptakes remained significantly depressed 48 h after exposure to 95% O2 had ended. Inhibition of intracellular metabolism of 5-HT by iproniazid did not affect 5-HT uptake by control or O2-exposed endothelial cells. High PO2 levels depress 5-HT uptake in endothelial cells by direct inhibition of the transcellular transport of 5-HT and hyperoxic depression of 5-HT uptake in cultured endothelial cells is not readily reversible.