Hypoxic pulmonary vascular remodeling in rats is associated with increased polyamine transport in pulmonary artery smooth muscle cells (PASMCs). We therefore defined constitutive and hypoxia-induced polyamine transport properties of rat cultured PASMCs and determined the impact of polyamine transport blockade on hypoxia-induced accumulation of p38 MAP kinase. PASMCs exhibited polyamine transport pathways that were characterized by Michaelis-Menten kinetics. RNA synthesis inhibition attenuated while inhibition of protein synthesis increased polyamine uptake, thus suggesting regulation by ornithine decarboxylase-antizyme. The presence of two transporters with overlapping selectivities, one for putrescine and another for all three polyamines, was inferred by cross-competition studies and by findings that only putrescine uptake was sodium dependent and that hypoxia caused a selective, time-dependent induction of putrescine transport. The pathophysiological significance of augmented putrescine import was suggested by the observation that polyamine transport inhibition suppressed hypoxia-induced p38 MAP kinase phosphorylation. These results indicate that rat PASMCs express two polyamine transporters and that a specific increase in the putrescine uptake pathway is necessary for hypoxia-induced activation of p38 MAP kinase.