KINETICS AND CELLULAR-LOCALIZATION OF PUTRESCINE UPTAKE IN HUMAN LUNG-TISSUE

Background-The polyamines (putrescine, spermidine, and spermine) are i nvolved in cellular growth, proliferation, and differentiation. In the lungs of various species, polyamines are accumulated by an active upt ake system which also mediates the uptake of cystamine and paraquat. I n the rat lung putrescine uptake has been shown to be cell-specific, o ccurring predominantly in the alveolar epithelium. The aim of this stu dy was to characterise the uptake of putrescine in human lung. Methods -Lung tissue was obtained from 31 patients undergoing surgery for lung cancer. Slices (0.7 mm thick) from non-tumour containing lung parench yma were incubated for 15-60 minutes in Krebs-Ringer phosphate buffer with various concentrations of putrescine (2.5 to 80 mu mol/l) contain ing 0.1 mu Ci [1,4-C-14]-putrescine. Uptake was assessed from tissue r adioactivity. For autoradiographic imaging, slices were incubated for 30 minutes with 2.5 mu mol/l putrescine containing 2.5 mCi [1,4n-H-3]- putrescine. Results-The accumulation of [C-14]-putrescine into slices was time-dependent and energy-dependent, and obeyed saturation kinetic s, with mean calculated values for V-max (maximal rate of uptake) of 4 14 nmol/g/hour and for K-m (medium concentration at which the rate of uptake is half V-max) of 7.2 mu mol/l, with a large interindividual va riation. Competitive inhibition was observed on incubation with cystam ine, which appears to have a high affinity for the uptake system since its calculated K-1 (concentration of inhibitor at which the K-m is do ubled) was 3.2 mu mol/l. Ultrastructural autoradiography showed labell ing over both type I and type II cells of the alveolar epithelium, but not over the endothelium or any cells of the interstitium. Alveolar m acrophages were also devoid of label. Conclusions-These results show t hat the human lung possesses an active uptake system for putrescine, a nd probably also cystamine, which is located in both cell types of the alveolar epithelium. These findings may be used to develop tests for the assessment of the alveolar epithelium.