Autoradiographic localization of putrescine uptake to type II pneumocytes of rabbit lung slices.

At low concentrations (0.4-5.0 microM), the polyamine, putrescine, is accumulated predominantly by a saturable process in rabbit lung slices. The question of why the lung should possess polyamine transport capabilities and the known cellular compartmentalization of various other pulmonary functions prompted us to investigate whether putrescine uptake was localized to a specific cell type(s) within rabbit lung. Localization of putrescine uptake in rabbit lung was investigated by frozen and plastic section autoradiography, combined with electron microscopy. Rabbit lung slices were incubated with [3H]putrescine at a concentration (0.4 microM) at which the saturable component of uptake predominates. Both frozen and plastic section autoradiograms revealed relatively minor amounts of radiolabel associated with either vascular or bronchiolar tissues, whereas a greater density of radiolabel was present over the alveolar epithelium. Highly localized areas of radiolabel were found at the junctions of adjacent alveoli and these labeled cells were identified by electron microscopy as type II pneumocytes. We conclude that the type II pneumocyte is a major site of putrescine uptake in rabbit lung slices. Our study also indicates that different rabbit lung cell types possess differing abilities to accumulate putrescine.