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

Abstract

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)

The mechanisms by which polyamines accelerate tumor spread

“…In cells exposed to chronic hypoxia, polyamine synthesis is decreased, while the ability to take up polyamines from the surroundings is increased [64,65]. Cells in a hypoxic environment have a resultant decrease in de novo polyamine synthesis and a concurrent increased capacity to take up polyamines from surrounding tissues, e.g.…”

Putrescine Uptake by Alveolar Epithelial Cell Monolayers Exhibiting Differing Transepithelial Electrical Resistances

“…25 Putrescine is accumulated by the lungs in an active manner that can be described by Michaelis-Menten kinetics. 25 The pulmonary epithelia cells responsible for this active uptake are Clara cells, in the bronchial epithelium, and type I and II alveolar cells in the lung parenchyma.…”

“…25 Putrescine is accumulated by the lungs in an active manner that can be described by Michaelis-Menten kinetics. 25 The pulmonary epithelia cells responsible for this active uptake are Clara cells, in the bronchial epithelium, and type I and II alveolar cells in the lung parenchyma. 26,27 Putrescine was accumulated by the cell monolayers exhibiting both high and low TEERs by a temperature-and concentration-dependent pathway that exhibited saturation kinetics.…”

Regulation of ornithine decarboxylase and polyamine import by hypoxia in pulmonary artery endothelial cells

“…Cells were seeded in 12well plastic plates (Corning) at 3 ϫ 10 5 cells/well and were grown to confluence. Polyamine uptake was determined as described previously (2)(3)(4). After incubation under the indicated conditions, cells were rinsed with serum-free DMEM after which 1 ml of DMEM was added to each well and the cells were allowed to acclimate for 30 min.…”