Role of ATP and sodium in polyamine transport in bovine pulmonary artery smooth cells

Abstract

Increased polyamine transport may be a key mechanism driving elevations in lung cell polyamine content necessary for the development of chronic hypoxic pulmonary hypertension. Bovine pulmonary artery smooth muscle cells (PASMCs) in culture exhibit two carriers for polyamines, a nonselective one shared by the three polyamines, putrescine (PUT), spermidine (SPD), and spermine (SPM), and another that is selective for SPD and SPM. Hypoxia appears to up-regulate both carriers. In this study, we examined the role of ATP and the Na + gradient in regulating polyamine transport in control PASMCs and in PASMCs with polyamine transport augmented by culture under hypoxic conditions (Po 2: 15–30 torr). Inhibition of ATP synthesis with dinitrophenol + iodoacetate profoundly reduced polyamine uptake in both control and hypoxic PASMCs. Putrescine uptake was somewhat more sensitive to iso-osmotic replacement of extracellular Na + with choline chloride or sucrose than were SPD or SPM in both hypoxic and standard cells, but under no conditions did Na + replacement substantially alter polyamine uptake. Treatment of PASMCs with ouabain, a Na +-K +ATPase inhibitor, or with gramicidin, a Na + ionophore, minimally attenuated polyamine transport, whereas the Na +/K + ionophore monensin increased polyamine uptake in standard, but not in hypoxic, cells. In general, the reduction in the extracellular Na + content or ionophore-induced increases in Na + permeability had a greater suppressive effect on polyamine transport in hypoxic cells than in standard cells, suggestive of the induction of Na +dependent polyamine carriers by hypoxia. These observations indicate that the activities of the two putative polyamine transport pathways in standard PASMCs, as well as their up- regulation by hypoxia, require ATP synthesis. In addition, it appears that polyamine transport in PASMCs is composed of two components: one a prominent sodium-independent transporter and the other a relatively minor component that is sodium dependent. The latter may be activated by hypoxic exposure in combination with the induction of new polyamine carriers.