Investigation of the transport of intact glutathione in human and rat typeII pneumocytes

The aim of the study was to investigate whether there is transmembrane tran sport of intact glutathione ([H-3]-GSH, 0.1 mu Ci) in rat and human type II pneumocytes (T2P), and if this transport might be dependent on the redox s tate of the extracellular fluid. The T2P were pretreated with acivicin (250 mu M) to inhibit gamma-glutamyl-transferase activity and with L-buthionine -[SR]-sulfoximine (1 mM) to inhibit intracellular GSH synthesis. After 48h in culture, initial GSH influx rate was 0.70 +/- 0.20 nmol/min/mg protein ( 37 degrees C) and 0.35 +/- 0.04 nmol/min/mg protein (4 degrees C) during th e first 5 min in rat T2P In human T2P, the initial GSH influx rate was 0.36 +/- 0.30 nmol/min/mg protein (37 degrees C) and 0.32 +/- 0.06 nmol/min/mg protein (4 degrees C) during the first 10 min. Thereafter no further influx was found. The influx of 1 mM GSH in freshly isolated rat and human T2P in suspension was 2.3 +/- 0.3 and 1.2 +/- 0.3 nmol/mg protein after 15 min at 37 degrees C, and 2.8 +/- 0.2 and 1.0 +/- 0.3 nmol/mg protein at 4 degrees C, respectively. When GSH influx was studied at different concentrations b etween 0 and 40 mM, a linear increase without saturation or difference betw een 37 degrees C and 4 degrees C was found. Preexposure to ouabain had no e ffect on GSH influx. Efflux of GSH was stimulated and influx inhibited by p reexposure of the cells to reduced thiols, while disulphides inhibited effl ux and favoured inward uptake. Thus, in human and rat T2P a GSH-carrier exi sts which operates as an effluxer. At GSH concentrations in the physiologic al range no uptake is seen, but some uptake can be observed at GSH concentr ations above normal physiological levels. The uptake appears to be energy-i ndependent and non-saturable. Efflux of GSH is stimulated and influx inhibi ted by reduced thiols, while disulphides inhibit the efflux and favour inwa rd uptake. GSH uptake in T2P thus may depend on concentration gradients and driving forces, such as the redox state of the extracellular fluid.