Putrescine uptake in hamster lung slices and primary cultures of type II pneumocytes

Abstract

Putrescine is accumulated in the lungs of various species by an active uptake system that also mediates the uptake of cystamine and paraquat. We have characterized this uptake in both lung slices and type II pneumocytes isolated from hamsters by trypsin digestion, differential adherence on plastic, and centrifugation on a discontinuous Percoll gradient. The accumulation of [14C]putrescine in lung slices was shown to be temperature and energy dependent, and to obey saturation kinetics, with mean calculated values of apparent Michaelis constant (Km) 29.4 microM and maximum rate of uptake (Vmax) 637 nmol.g-1.h-1. In the presence of cystamine or paraquat, the putrescine uptake was reduced in a manner compatible with competitive inhibition. The calculated inhibitor constants (Ki) were 16 and 1,017-1,328 microM for the inhibition by cystamine and paraquat, respectively. The cellular localization of [3H]putrescine in lung slices after incubation with 2.5 microM putrescine was determined by light-microscopic autoradiography. Labeling was present in type II and possibly also in type I pneumocytes of the alveolar epithelium but not in macrophages, endothelium, or cells of the interstitium. Two days after their isolation, cultured type II pneumocytes exhibited an uptake of putrescine that had kinetic characteristics similar to those of slices (Km of 23 microM and Vmax of 3.06 mumol.g protein-1.h-1) and was also competitively inhibited by paraquat (Ki of 222-350 microM paraquat). Our data demonstrate the presence of an active uptake system for putrescine in both lung slices and cultured type II pneumocytes.(ABSTRACT TRUNCATED AT 250 WORDS)