Multiple polyamine transport pathways in cultured pulmonary artery smooth muscle cells: regulation by hypoxia

The polyamines putrescine (PUT), spermidine (SPD), and spermine (SPM) are a family of low molecular weight organic cations that play essential intracellular regulatory roles in cell growth and differentiation. Consistent with this important function, increases in cellular polyamine contents are necessary for a variety of physiologic and pathologic events in the lung, including development of hypertensive pulmonary vascular disease secondary to chronic alveolar hypoxia. In intact rat lungs, hypoxia depresses ornithine decarboxylase activity, the initial rate-limiting enzyme in de novo polyamine synthesis, and enhances uptake of PUT from the vascular compartment, thus suggesting that increased polyamine transport is the driving mechanism behind hypoxia-induced increases in lung polyamine contents. Cultured bovine pulmonary artery smooth muscle cells (PASMCs) also express a transport system for SPD that is augmented by culture under hypoxic conditions. Because there may be multiple uptake pathways that are relatively selective for specific polyamines, the present study determined whether cultured bovine PASMCs expressed discrete transporters for [14C]PUT, [14C]SPD, and [14C]SPM, and whether they were differentially regulated by hypoxia. [14C]PUT, [14C]SPD, and [14C]SPM transport was examined in PASMCs cultured under "standard" (culture medium PO2: > 100 torr), "normoxic" (culture medium PO2: 50 to 70 torr), or "hypoxic" (culture medium PO2: 18 to 30 torr) conditions. Uptake of all three [14C]polyamines in cells cultured under standard conditions was temperature- and concentration-dependent, exhibited saturation kinetics, and could be modeled by Michaelis-Menten kinetics. In hypoxic PASMCs, values of Vmax for PUT, SPD, and SPM uptake increased by 3-, 2-, and 2-fold, respectively, relative to cells cultured under normoxic or standard incubator conditions.(ABSTRACT TRUNCATED AT 250 WORDS)