Role of Low Ouabain-Sensitive Isoform of Na+-K+-ATPase in the Regulation of Basal Tone and Agonist-Induced Contractility in Ovine Pulmonary Artery

Comprehensive analysis identified a reduction in ATP1A2 mediated by ARID3A in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by abdominal aorta dilatation and progressive structural impairment and is usually an asymptomatic and potentially lethal disease with a risk of rupture. To investigate the underlying mechanisms of AAA initiation and progression, seven AAA datasets related to human and mice were downloaded from the GEO database and reanalysed in the present study. After comprehensive bioinformatics analysis, we identified the enriched pathways associated with inflammation responses, vascular smooth muscle cell (VSMC) phenotype switching and cytokine secretion in AAA. Most importantly, we identified ATPase Na⁺/K⁺ transporting subunit alpha 2 (ATP1A2) as a key gene that was significantly decreased in AAA samples of both human and mice; meanwhile, its reduction mainly occurred in VSMCs of the aorta; this finding was validated by immunostaining and Western blot in human and mouse AAA samples. Furthermore, we explored the potential upstream transcription factors (TFs) that regulate ATP1A2 expression. We found that the TF AT‐rich interaction domain 3A (ARID3A) bound the promoter of ATP1A2 to suppress its expression. Our present study identified the ARID3A‐ATP1A2 axis as a novel pathway in the pathological processes of AAA, further elucidating the molecular mechanism of AAA and providing potential therapeutic targets for AAA.

Evaluation of potential sodium-iodide symporter (NIS) inhibitors using a secondary Fischer rat thyroid follicular cell (FRTL-5) radioactive iodide uptake (RAIU) assay

The Fischer rat thyroid follicular cell line (FRTL-5) endogenously expresses the sodium-iodide symporter (NIS) and has been used to identify environmental chemicals that perturb thyroid hormone homeostasis by disruption of NIS-mediated iodide uptake. Previously, a high-throughput radioactive iodide uptake (RAIU) screening assay incorporating the hNIS-HEK293T-EPA cell line was used to identify potential human NIS (hNIS) inhibitors in 1028 ToxCast Phase I (ph1_v2) and Phase II chemicals. In this study, the FRTL-5 cell line was evaluated and applied as a secondary RAIU assay coupled with cell viability assays to further prioritize highly active NIS inhibitors from the earlier screening. Assay validation with ten reference chemicals and performance assessment by chemical controls suggest the FRTL-5 based assays are robust and highly reproducible. Top-ranked chemicals from the ToxCast screening were then evaluated in both FRTL-5 and hNIS RAIU assays using newly sourced chemicals to strengthen the testing paradigm and to enable a rat vs. human species comparison. Eighteen of 29 test chemicals showed less than 1 order of magnitude difference in IC₅₀ values between the two assays. Notably, two common perfluorinated compounds, perfluorooctanesulfonic acid (PFOS) and perfluorohexane sulfonate (PFHxS), demonstrated strong NIS inhibitory activity [IC₅₀ - 6.45 (PFOS) and - 5.70 (PFHxS) log M in FRTL-5 RAIU assay]. In addition, several chemicals including etoxazole, methoxyfenozide, oxyfluorfen, triclocarban, mepanipyrim, and niclosamide also exhibited NIS inhibition with minimal cytotoxicity in both assays and are proposed for additional testing using short-term in vivo assays to characterize effects on thyroid hormone synthesis.

Vasorelaxation of goat mesenteric artery is mediated by endothelial Na(+)-K(+)-ATPase

OBJECTIVE

To examine the role of Na(+)-K(+)-ATPase and K(+) channels in mediating vasorelaxation in the superior mesenteric artery of Capra hircus.

MATERIALS AND METHODS

Goat superior mesenteric artery (GSMA) was cut into 1.5-2 mm circular rings and mounted in a thermostatically controlled (37°C ± 0.5°C) organ bath containing 20 ml of modified Krebs-Henseleit saline (MKHS) (pH 7.4), with continuous aeration under 1.5 g tension for 90 min. Endothelium-intact (ED+) or endothelium-denuded (ED-) GSMA ring was contracted with phenylephrine (PE) or 5-hydroxytryptamine (5-HT) (1 μM-0.1 mM) in the absence or presence of ouabain (0.1 μM). KCl (1 μM-10 mM) was added cumulatively to K(+)-free MKHS-pre-contracted (ED+/-) rings in the absence or presence of ouabain (0.1 μM) or barium (1 μM) or 4-aminopyridine (1 μM).

RESULTS

Ouabain did not alter the basal tone of the arterial ring. The contractile response induced by PE (Emax: 50.46 ± 2.68, pD2: 5.53 ± 0.04) and 5-HT (Emax: 30.86 ± 1.33, pD2: 6.17 ± 0.03) in ED+ ring was significantly (P < 0.001) augmented in ED- rings (PE: Emax: 93.30 ± 2.11, pD2: 6.41 ± 0.04; 5-HT: Emax: 95.07 ± 0.99, pD2: 6.27 ± 0.03). The contractile response induced by PE and 5-HT in ED+ or ED- rings in the presence of ouabain was almost identical with that of ED- rings. Vasorelaxation of KCl (Emax: 2.90 ± 1.14, pD2: 3.9 ± 0.03) was significantly attenuated in the presence of ouabain (Emax: 73.8 ± 5.16, pD2: 4.3 ± 0.04), Ba(2+) (Emax: 16.34 ± 4.7, pD2: 3.22 ± 0.02), 4-AP (Emax: 18.16 ± 2.4, pD2: 3.68 ± 0.03), ouabain and Ba(2+) (Emax: 70.09 ± 3.66, pD2: 4.41 ± 0.04), and ouabain and 4-AP (Emax: 66.98 ± 4.61, pD2: 4.13 ± 0.06).

CONCLUSION

The vasorelaxation in GSMA is mediated by the endothelium-derived hyperpolarizing factor (EDHFs) such as ouabain-sensitive Na(+)-K(+)-ATPase, KIR and Kv channels.

Endothelial and smooth muscle cell ion channels in pulmonary vasoconstriction and vascular remodeling

The pulmonary circulation is a low resistance and low pressure system. Sustained pulmonary vasoconstriction and excessive vascular remodeling often occur under pathophysiological conditions such as in patients with pulmonary hypertension. Pulmonary vasoconstriction is a consequence of smooth muscle contraction. Many factors released from the endothelium contribute to regulating pulmonary vascular tone, while the extracellular matrix in the adventitia is the major determinant of vascular wall compliance. Pulmonary vascular remodeling is characterized by adventitial and medial hypertrophy due to fibroblast and smooth muscle cell proliferation, neointimal proliferation, intimal, and plexiform lesions that obliterate the lumen, muscularization of precapillary arterioles, and in situ thrombosis. A rise in cytosolic free Ca(2+) concentration ([Ca(2+)]cyt) in pulmonary artery smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction, while increased release of mitogenic factors, upregulation (or downregulation) of ion channels and transporters, and abnormalities in intracellular signaling cascades are key to the remodeling of the pulmonary vasculature. Changes in the expression, function, and regulation of ion channels in PASMC and pulmonary arterial endothelial cells play an important role in the regulation of vascular tone and development of vascular remodeling. This article will focus on describing the ion channels and transporters that are involved in the regulation of pulmonary vascular function and structure and illustrating the potential pathogenic role of ion channels and transporters in the development of pulmonary vascular disease.

Arachidonic acid inhibits Na⁺-K⁺-ATPase via cytochrome P-450, lipoxygenase and protein kinase C-dependent pathways in sheep pulmonary artery

The purpose of the study was to examine whether arachidonic acid inhibits vascular Na(+)-K(+)-ATPase in pulmonary vasculature and if so, what are the mechanisms involved. Functional Na(+)-K(+)-ATPase activity was studied in terms of K(+)-induced relaxation in sheep pulmonary arterial rings contracted with K(+)-free solution and 5-HT. Arachidonic acid (10-100 μM) caused concentration-dependent inhibition of KCl-induced relaxations and also increased basal arterial tone. Cytochrome P-450 inhibitor, 17-octadecynoic acid (17-ODYA) completely reversed the arachidonic acid (30 μM)-induced inhibition of KCl relaxation. Further, in the presence of HET0016, a selective blocker of 20-hydroxyeicosatetraenoic acid (20-HETE), arachidonic acid-induced inhibition of KCl relaxation was not evident. Accordingly, 20-HETE, a cytochrome P-450 metabolite of arachidonic acid, also significantly attenuated KCl-induced relaxations. Norhydihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, however, partially restored the relaxation to K(+), impaired in the presence of arachidonic acid (30 μM). On the other hand, cyclooxygenase inhibitor indomethacin failed to reverse the inhibitory effect of arachidonic acid on KCl-induced relaxation. Staurosporin, a protein kinase C inhibitor, completely reversed the inhibitory effect of arachidonic acid and 20-HETE on K(+)-induced relaxation. In conclusion, the results suggest that 20-HETE, a cytochrome P-450 metabolite of arachidonic acid has a predominant role in the inhibition of functional Na(+)-K(+)-ATPase activity in the sheep pulmonary artery, while the lipooxygenase pathway has a secondary role. It is also evident that protein kinase C is involved in the inhibition of Na(+)-K(+)-ATPase by arachidonic acid/20-HETE in sheep pulmonary artery.

Evaluation of effects of eicosapentaenoic acid on Na⁺-K⁺-ATPase in sheep pulmonary artery

In the present study, we have evaluated the effects of eicosapentaenoic acid (EPA) on Na(+)-K(+)-ATPase in sheep pulmonary artery. Acute (30 min) and prolonged (24 h) exposure of arterial rings to EPA (30 μM) significantly decreased potassium chloride (KCl)-induced relaxation, an index of functional Na(+)-K(+)-ATPase activity. In acute exposure, the pD(2) and E (max) (the maximal response) values for KCl-induced relaxation were 3.21 ± 0.33 and 61.58 ± 11.30% (n = 5) versus control 3.58 ± 0.07 and 82.44 ± 2.36% (n = 24), respectively. The pD(2) and E (max) values for KCl-induced relaxation in arterial rings exposed to EPA for 24 h in organ culture were 2.52 ± 0.11 and 55.00 ± 5.72% versus control 3.04 ± 0.19 and 80.74 ± 11.96%, respectively; n = 4. Exposure of the arterial rings to EPA (30 μM) for 24 h in organ culture, significantly decreased (17.58 ± 2.15%) the protein expression of α(1) isoform of Na(+)-K(+)-ATPase. Acute exposure to EPA for 30 min significantly decreased (21.06 ± 5.89%) the Na(+)-K(+)-ATPase activity as measured by inorganic phosphate (Pi) release. EPA, up to 100 μM concentration, marginally (<10% of 80 mM KCl contraction) increased the basal tone of the pulmonary artery. Additionally, EPA (10-30 μM) had no effect on Mg(2+)-ATPase activity as well as on cyclic guanosine monophosphate (cGMP) production. All these results show that EPA has inhibitory effect on Na(+)-K(+)-ATPase in sheep pulmonary artery but prolonged exposure had no additional effect on sodium pump, and EPA-induced inhibition of Na(+)-K(+)-ATPase may be due to attenuation in protein expression of α(1) isoform of Na(+)-K(+)-ATPase independent of cGMP production.

Eicosapentaenoic acid-induced endothelium-dependent and -independent relaxation of sheep pulmonary artery

It is known that long chain polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), have beneficial effects on cardiovascular function including pulmonary hypertension. The purpose of the present study was to examine the mechanisms involved in EPA-induced relaxation of sheep isolated pulmonary artery by measuring isometric tension. Nitric oxide (NO) derived from constitutive nitric oxide synthase (cNOS) was measured by Greiss method in the presence of the inducible nitric oxide synthase (iNOS) selective inhibitor N-[[3-(aminomethyl) phenyl]methyl]-ethanimidamide, dihydrochloride (1400 W). EPA (10(-)(7)-10(-)(4)M) caused concentration-dependent relaxation of sheep pulmonary artery with a pD(2) of 5.56+/-0.09 and E(max) of 87.40+/-3.10% (n=9). N(G)-nitro-L-arginine methyl ester (L-NAME) 100 microM significantly attenuated (E(max) 41.95+/-6.70%; n=8) EPA-induced relaxation of endothelium intact arterial rings. Similarly, endothelium denudation markedly inhibited (E(max) 17.60+/-1.21%; n=4) EPA-induced relaxation. EPA (30 microM) significantly increased the cNOS-derived NO release (10.17+/-0.96; n=8 versus control 7.43+/-0.78 pmol/mg tissue wet wt./h; n=7) in endothelium intact vessels. However, EPA-stimulated NO release was markedly blunted by either 100 microM L-NAME (7.07+/-0.54 pmol/mg tissue wet wt./h; n=8) or endothelium removal (6.97+/-0.87 pmol/mg tissue wet wt./h; n=17). In endothelium-denuded K(+) (80 mM)-depolarized arterial rings, EPA (30 microM) significantly inhibited CaCl(2)-induced contractions (E(max) 42.77+/-5.90% versus control 94.78+/-9.82%; n=5). The fatty acid also inhibited nifedipine (1 microM)-insensitive 5-HT-induced contractions in this vessel (E(max) 70.57+/-4.88% versus control 161.50+/-17.46%; n=5). In conclusion, EPA relaxes sheep pulmonary artery primarily through endothelium-dependent NO release, and the residual endothelium-independent relaxation may result from inhibition of Ca(2+)-influx through L-type calcium channels, as well as 5-HT-stimulated intracellular Ca(2+) release.