7 KCl, 25 NaHCO3, 2.5 CaCl2·2H2O, 1.2 KH2PO4, 1.2 MgSO4·7H2O, 11 glucose, and 0.01 EDTA), gassed with 95% O2 and 5% CO2, at 37 °C and pH 7.4. The preparations were equilibrated under a resting tension of 0.5 g for up to 45 min. Isometric tension was recorded using an isometric force transducer (Letica TRI 210, Spain) connected to an acquisition system (MP100, BiopacSystems, USA). After the equilibration period, rings were exposed to 75 mM KCl to assess the maximal tension developed. Following the wash, concentration-response curves to the α1-adrenergic receptor agonist phenylephrine (10−10–10−5 M,

Sigma–Aldrich, Germany) were obtained. Both the maximal contractile responses to 75 mM KCl and to phenylephrine were PS-341 concentration not modified LBH589 by PM2.5 in the pulmonary artery. In addition, the endothelium-dependent relaxation induced by acetylcholine (10−9–10−5 M, Sigma–Aldrich) or the relaxation induced by the NO donor sodium nitroprusside (10−10–10−6 M, Sigma–Aldrich) were evaluated in rings contracted with phenylephrine (0.1 μM). The oxidative fluorescent dye hydroethidine, which produces a red fluorescence signal when oxidized to ethidium bromide, was used to evaluate the in situ production of reactive oxygen species (ROS) in the vascular tissue, as previously described ( Camporez et al., 2011). Briefly, transverse sections (10 μm) of extralobar pulmonary arteries obtained in a cryostat were incubated

at 37 °C for 30 min in Krebs-HEPES buffer (in mM: 130 NaCl, 5.6 KCl, 2 CaCl2, 0.24 MgCl2, 8.3 HEPES, and 11 glucose, pH 7.4). Then, fresh buffer containing hydroethidine (2 μM) was topically applied to each tissue section and the slides were incubated in a light-protected humidified chamber at 37 °C for 30 min. Negative control sections received the same volume of phosphate buffer without hydroethidine. In some experiments, parallel sections were incubated with polyethylene glycol-superoxide dismutase (PEG-SOD, 500 U/mL, Sigma–Aldrich), a membrane-permeable specific scavenger of superoxide anions, to verify the Thiamet G DHE fluorescence dependent on superoxide anion

formation (Jiménez-Altayó et al., 2006). Images were obtained with an optical microscope (Axioskop, Zeiss, Germany) equipped with a filter to rhodamine and a camera (ZVS-3C75DE, Zeiss) using an objective for fluorescence (20×). For fluorescence quantification, four areas per ring were sampled for each experimental condition. The integrated optical densities were calculated using Image J software (NIH, USA). Protein extracts (75 μg) of extralobar pulmonary arteries were electrophoretically separated by SDS-PAGE and then transferred to polyvinylidene difluoride membranes (Amersham, USA) overnight at 4 °C using a Mini Trans-Blot Cell system (Bio-Rad, USA) containing 25 mmol/L Tris, 190 mmol/L glycine, 20% methanol, and 0.05% SDS, as previously described (Davel et al., 2008).