Putrescine uptake in rat type II pneumocytes correlates with gamma-glutamyltransferase activity

gamma-Glutamyltransferase (gamma GT) is a key enzyme in glutathione metabolism and it is thought also to play a role in the uptake of polyamines such as putrescine. The aim of our study was to investigate if changes in gamma GT activity would alter total putrescine uptake [P(up)(tot)], as well as more specific uptake via the gamma GT pathway [P(up)(gamma GT)]. Forty-eight hours after their isolation, rat type II cells were exposed to 30, 60 or 125 microM L-buthionine-[SR]-sulfoximine (BSO) for 3 hr; 200 or 800 microM tertiary-butylhydroperoxide (t-BOOH) for 40 min; 10, 100 or 1000 microM paraquat (PQ) for 1 hr; and 60 or 85% O2 for 48 hr. The gamma GT activity, P(up)(tot) and P(up)(gamma GT) (assessed by inhibiting gamma GT) were measured immediately after the exposure to hyperoxia, or 24 hr after treatment with BSO, t-BOOH or PQ. From previous studies, it is known that these experimental conditions increased (BSO, 200 microM t-BOOH) or decreased (800 microM t-BOOH, PQ, hyperoxia) gamma GT activity. There was a strong correlation between the changes in gamma GT activity and the changes in P(up)(gamma GT) (r = 0.81, p < 0.001). These findings support the hypothesis that gamma GT partly regulates the uptake of putrescine, one of the polyamines required for cell growth and differentiation.