Role of gamma-glutamyltransferase in putrescine uptake by rat type II pneumocytes.
Putrescine uptake in type II pneumocytes is a carrier-mediated active process. Our hypothesis was that oligoamines might be taken up into the cell at least in part by gamma-glutamyltransferase (gamma-GT). This was investigated in rat type II pneumocytes 24 hr after their isolation. Preexposure to 125 microM L-buthionine-[SR]-sulfoximine (BSO) or 100 microM diethylmaleate (DEM), both of which affect intracellular glutathione (GSH) only, were found to decrease GSH by 85% (p < 0.05) and 62%, respectively (p < 0.05), without change in [3H]-putrescine uptake. Preexposure to 20 microM N-ethylmaleimide (NEM), which affects intra- and extracellular GSH, decreased intracellular GSH by 79% (p = 0.015) and putrescine uptake by 39% (p = 0.03). Selective extracellular GSH depletion by 10 microM copper-o-phenanthroline complex (CuP) led to a decrease in putrescine uptake of 41% (p = 0.001), while intracellular GSH remained unchanged. Specific inhibition of gamma-GT by 5-20 mM serine-borate or 5 mM acivicin gave similar degrees of putrescine uptake inhibition (39.5% and 40.5%). The kinetic properties of the putrescine uptake system in the presence of acivicin and serine-borate indicated that the Vmax decreased by 25%, while Km remained unchanged. In experiments with pure gamma-GT, the oligoamines putrescine, spermidine and spermine, and cystamine proved to be acceptor substrates for gamma-GT, all having similar efficiencies (Vmax/Km); methylglyoxal-bis-(guanyl-hydrazone) and paraquat were not accepted. As extracellular GSH is required for gamma-GT, and because its extracellular depletion inhibits putrescine uptake as much as specific inhibition of gamma-GT, we suggest that 30-40% of the putrescine uptake in type II pneumocytes occurs by gamma-GT and that, therefore, at least two systems are involved in the uptake of putrescine.
van Klaveren
R J
RJ
Laboratory of Pneumology, K.U.Leuven, Belgium.
Hoet
P H
PH
Demedts
M
M
Nemery
B
B
D000818:Animals; D001881:Borates / Q000494:pharmacology; D002469:Cell Separation; D002470:Cell Survival; D002478:Cells, Cultured; D003300:Copper; D015536:Down-Regulation; D005978:Glutathione / Q000378:metabolism / Q000494:pharmacology; D007555:Isoxazoles / Q000494:pharmacology; D007700:Kinetics; D008168:Lung / Q000378:metabolism*; D008297:Male; D009942:Organometallic Compounds / Q000494:pharmacology; D010618:Phenanthrolines / Q000494:pharmacology; D011700:Putrescine / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012694:Serine / Q000494:pharmacology; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D001881:Borates; D007555:Isoxazoles; D009942:Organometallic Compounds; D010618:Phenanthrolines; C040900:serine-borate complex; C014741:bis(1,10-phenanthroline)copper(2+) ion; D012694:Serine; D003300:Copper; D005723:gamma-Glutamyltransferase; D005978:Glutathione; C006303:acivicin; D011700:Putrescine