The effects of endotoxin on glutamine transport by pulmonary artery endothelial cells

The effects of endotoxin on glutamine transport by cultured pulmonary artery endothelial cells (PAECs) were studied in order to gain further insight into the regulation of the altered lung glutamine metabolism that characterizes severe infection. Incubation of PAECs with endotoxin (1 micrograms/ml) resulted in a significant increase in System ASC-mediated glutamine transport which did not occur for 8 hr and was maximal after 12 hr of exposure. Kinetic studies indicated that the increase in carrier-mediated activity was not due to a change in Km (101 +/- 6 microM in controls vs 97 +/- 4 microM in endotoxin-treated cells, P = NS), but rather to a 73% increase in Vmax (840 +/- 60 pmole/mg protein/30 sec in controls vs 1450 +/- 80 in endotoxin-treated cells, P less than 0.001). The increase in glutamine uptake by PAECs was completely blocked by actinomycin D and cycloheximide, indicating that the accelerated glutamine transport was most probably due to an increase in transporter synthesis. Endotoxin stimulates glutamine uptake by PAECs, either directly or indirectly, an adaptive response which may be necessary to support cellular metabolism, structure, and function.