González Paula Mariela, Rocchetta Iara, Abele Doris, Rivera-Ingraham Georgina A
Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Fisicoquímica, Buenos Aires, Argentina.
Instituto de Bioquímica y Medicina Molecular (IBIMOL), CONICET-Universidad de Buenos Aires, Buenos Aires, Argentina.
Front Physiol. 2019 Mar 5;9:1709. doi: 10.3389/fphys.2018.01709. eCollection 2018.
Intertidal experience rapid transgression to hypoxia when they close their valves during low tide. This induces a physiological stress response aiming to stabilize tissue perfusion against declining oxygen partial pressure in shell water. We hypothesized that nitric oxide (NO) accumulation supports blood vessel opening in hypoxia and used live imaging techniques to measure NO and superoxide anion ( ) formation in hypoxia-exposed gill filaments. Thirty minutes of moderate (7 kPa pO) and severe hypoxia (1 kPa pO) caused 1.6- and 2.4-fold increase, respectively, of NO accumulation in the endothelial muscle cells of the hemolymphatic vessels of the gill filaments. This led to a dilatation of blood vessel diameter by 43% (7 kPa) and 56% (1 kPa), which facilitates blood flow. Experiments in which we applied the chemical NO-donor Spermine NONOate (concentrations ranging from 1 to 6 mM) under normoxic conditions corroborate the dilatational effect of NO on the blood vessel. The formation of within the filament epithelial cells increased 1.5 (7 kPa) and 2-fold (1 kPa) upon treatment. Biochemical analysis of mitochondrial electron transport complexes in hypoxia-exposed gill tissue indicates decreased activity of complexes I and III in both hypoxic conditions; whereas complex IV (cytochrome-c oxidase) activity increased at 7 kPa and decreased at 1 kPa compared to normoxic exposure conditions. This corresponds to the pattern of pO-dependent gill respiration rates recorded in experiments. Severe hypoxia (1 kPa) appears to have a stabilizing effect on NO accumulation in gill cells, since less O is available for NO oxidation to nitrite/nitrate. Hypoxia thus supports the NO dependent inhibition of complex IV activity, a mechanism that could fine tune mitochondrial respiration to the local O availability in a tissue. Our study highlights a basal function of NO in improving perfusion of hypoxic invertebrate tissues, which could be a key mechanism of tolerance toward environmental O variations.
潮间带生物在退潮时关闭瓣膜会迅速经历向缺氧状态的转变。这会引发一种生理应激反应，旨在针对壳内水中氧分压下降来稳定组织灌注。我们推测一氧化氮（NO）的积累有助于在缺氧状态下打开血管，并使用活体成像技术来测量暴露于缺氧环境的鳃丝中NO和超氧阴离子（ ）的形成。30分钟的中度（7 kPa pO）和重度缺氧（1 kPa pO）分别导致鳃丝血淋巴血管内皮肌细胞中NO积累增加1.6倍和2.4倍。这导致血管直径分别扩张43%（7 kPa）和56%（1 kPa），从而促进了血液流动。我们在常氧条件下应用化学NO供体精胺亚硝基铁氰化钠（浓度范围为1至6 mM）的实验证实了NO对血管的扩张作用。处理后，丝状体上皮细胞内的 形成增加了1.5倍（7 kPa）和2倍（1 kPa）。对暴露于缺氧环境的鳃组织中线粒体电子传递复合物的生化分析表明，在两种缺氧条件下，复合物I和III的活性均降低；而与常氧暴露条件相比，复合物IV（细胞色素c氧化酶）的活性在7 kPa时增加，在1 kPa时降低。这与在 实验中记录的依赖于pO的鳃呼吸速率模式相对应。重度缺氧（1 kPa）似乎对鳃细胞中NO的积累具有稳定作用，因为用于将NO氧化为亚硝酸盐/硝酸盐的O较少。因此，缺氧支持了NO对复合物IV活性的依赖性抑制，这一机制可将线粒体呼吸精确调节至组织中的局部O可用性。我们的研究突出了NO在改善缺氧无脊椎动物组织灌注方面的基础功能，这可能是对环境O变化耐受性的关键机制。
