Mechanism of putrescine transport in human pulmonary artery endothelial cells.

Effective lung repair requires optimal replication of critical cell populations in the lung. Endogenous polyamines such as putrescine, spermidine and spermine play important roles in cell proliferation and differentiation, and may arise due to intracellular synthesis or transport into the cell. To determine the mechanism of polyamine transport in lung endothelial cells, the uptake of putrescine in human pulmonary artery endothelial cells was examined. Putrescine (7 nM) uptake into the cells approached equilibrium at 1 hr and was inhibited by methylglyoxal bis(guanylhydrazone). Kinetic studies revealed that uptake occurred via both a high- and low-affinity system. The effect of several amines (700 microM) on the 15-min uptake of putrescine was examined and a rank order of inhibition was determined: methylglyoxal bis(guanylhydrazone) > putrescine > spermine > spermidine > gentamicin > mepiperphenidol. alpha-Aminoisobutyric acid, a prototype system A amino acid, and tetraethylammonium, an organic cation, had no effect. N-ethylmaleimide inhibited transport 71%, whereas dinitrophenol did not. A reduction in temperature from 37 degrees C to 5 degrees C resulted in a 42% decrease in putrescine transport. Additionally, removing fetal bovine serum from the uptake medium reduced transport 38%. These data indicate that human pulmonary artery endothelial cells possess a specific transport system for polyamines. An improved understanding of this pathway in pulmonary endothelial cells may permit development of strategies to facilitate growth and repair of this critical cell population.