Department of Pharmacology and Pharmacy, University of Hong Kong, Hong Kong.
Am J Physiol Heart Circ Physiol. 2011 Dec;301(6):H2313-21. doi: 10.1152/ajpheart.00258.2011. Epub 2011 Oct 7.
The present study investigated the mechanism underlying the transient potentiation of vasoconstriction by hypoxia in isolated porcine coronary arteries. Isometric tension was measured in rings with or without endothelium. Hypoxia (Po(2) <30 mmHg) caused a transient further increase in tension (hypoxic augmentation) in contracted (with U46619) preparations. The hypoxic response was endothelium dependent and abolished by inhibitors of nitric oxide synthase [N(ω)-nitro-L-arginine methyl ester (L-NAME)] or soluble guanylyl cyclase (ODQ and NS2028). The addition of DETA NONOate (nitric oxide donor) in the presence of L-NAME restored the hypoxic augmentation, suggesting the involvement of the nitric oxide pathway. However, the same was not observed after incubation with 8-bromo-cyclic GMP, atrial natriuretic peptide, or isoproterenol. Assay of the cyclic GMP content showed no change upon exposure to hypoxia in preparations with and without endothelium. Incubation with protein kinase G and protein kinase A inhibitors did not inhibit the hypoxic augmentation. Thus the hypoxic augmentation is dependent on nitric oxide and soluble guanylyl cyclase but independent of cyclic GMP. The hypoxic augmentation persisted in calcium-free buffer and in the presence of nifedipine, ruling out a role for extracellular calcium influx. Hypoxia did not alter the intracellular calcium concentration, as measured by confocal fluorescence microscopy. This observation and the findings that hypoxic augmentation is enhanced by thapsigargin (sarco/endoplasmic reticulum calcium ATPase inhibitor) and inhibited by HA1077 or Y27632 (Rho kinase inhibitors) demonstrate the involvement of calcium sensitization in the phenomenon.
本研究旨在探讨缺氧诱导离体猪冠状动脉短暂血管收缩增强的机制。通过环法测量有或无内皮的血管环的等长张力。缺氧（Po(2) <30mmHg）会导致收缩（用 U46619 处理）的血管环张力进一步短暂增加（缺氧增强）。这种缺氧反应是内皮依赖性的，可被一氧化氮合酶抑制剂[N(ω)-硝基-L-精氨酸甲酯（L-NAME）]或可溶性鸟苷酸环化酶抑制剂（ODQ 和 NS2028）消除。在 L-NAME 存在下加入 DETA NONOate（一氧化氮供体）可恢复缺氧增强，表明涉及一氧化氮途径。然而，在孵育过程中加入 8-溴环鸟苷酸、心钠素或异丙肾上腺素后，并没有观察到这种情况。在有和没有内皮的血管环中，暴露于缺氧后，环鸟苷酸含量的测定没有变化。蛋白激酶 G 和蛋白激酶 A 抑制剂的孵育并不能抑制缺氧增强。因此，缺氧增强依赖于一氧化氮和可溶性鸟苷酸环化酶，但不依赖于环鸟苷酸。在无钙缓冲液中和在硝苯地平存在下，缺氧增强仍然存在，排除了细胞外钙内流的作用。缺氧并没有改变细胞内钙浓度，如通过共聚焦荧光显微镜测量的那样。这一观察结果以及缺氧增强被 thapsigargin（肌浆内质网钙 ATP 酶抑制剂）增强以及被 HA1077 或 Y27632（Rho 激酶抑制剂）抑制的发现表明，钙敏化参与了这一现象。
