ROLE OF ATP AND SODIUM IN POLYAMINE TRANSPORT IN BOVINE PULMONARY-ARTERY SMOOTH CELLS

Increased polyamine transport may be a key mechanism driving elevation s in lung cell polyamine content necessary for the development of chro nic hypoxic pulmonary hypertension. Bovine pulmonary artery smooth mus cle cells (PASMCs) in culture exhibit two carriers for polyamines, a n onselective one shared by the three polyamines, putrescine (PUT), sper midine (SPD), and spermine (SPM), and another that is selective for SP D and SPM. Hypoxia appears to up-regulate both carriers. In this study , we examined the role of ATP and the Na+ gradient in regulating polya mine transport in control PASMCs and in PASMCs with polyamine transpor t augmented by culture under hypoxic conditions (Po-2: 15-30 ton). Inh ibition of ATP synthesis with dinitrophenol + iodoacetate profoundly r educed polyamine uptake in both control and hypoxic PASMCs. Putrescine uptake was somewhat more sensitive to iso-osmotic replacement of extr acellular Na+ with choline chloride or sucrose than were SPD or SPM in both hypoxic and standard cells, but under no conditions did Na+ repl acement substantially alter polyamine uptake. Treatment of PASMCs with ouabain, a Na+-K(+)ATPase inhibitor, or with gramicidin, a Na+ ionoph ore, minimally attenuated polyamine transport, whereas the Na+/K+ iono phore monensin increased polyamine uptake in standard, but not in hypo xic, cells. In general, the reduction in the extracellular Naf content or ionophore-induced increases in Nai permeability had a greater supp ressive effect on polyamine transport in hypoxic cells than in standar d cells, suggestive of the induction of Na+-dependent polyamine carrie rs by hypoxia. These observations indicate that the activities of the two putative polyamine transport pathways in standard PASMCs, as well as their upregulation by hypoxia, require ATP synthesis. In addition, it appears that polyamine transport in PASMCs is composed of two compo nents: 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 ne w polyamine carriers.