Evans A Mark, Mustard Kirsteen J W, Wyatt Christopher N, Peers Chris, Dipp Michelle, Kumar Prem, Kinnear Nicholas P, Hardie D Grahame
Division of Biomedical Sciences, School of Biology, Bute Building, University of St. Andrews, St. Andrews, Fife KY16 9TS, United Kingdom.
J Biol Chem. 2005 Dec 16;280(50):41504-11. doi: 10.1074/jbc.M510040200. Epub 2005 Sep 30.
Specialized O2-sensing cells exhibit a particularly low threshold to regulation by O2 supply and function to maintain arterial pO2 within physiological limits. For example, hypoxic pulmonary vasoconstriction optimizes ventilation-perfusion matching in the lung, whereas carotid body excitation elicits corrective cardio-respiratory reflexes. It is generally accepted that relatively mild hypoxia inhibits mitochondrial oxidative phosphorylation in O2-sensing cells, thereby mediating, in part, cell activation. However, the mechanism by which this process couples to Ca2+ signaling mechanisms remains elusive, and investigation of previous hypotheses has generated contrary data and failed to unite the field. We propose that a rise in the cellular AMP/ATP ratio activates AMP-activated protein kinase and thereby evokes Ca2+ signals in O2-sensing cells. Co-immunoprecipitation identified three possible AMP-activated protein kinase subunit isoform combinations in pulmonary arterial myocytes, with alpha1 beta2 gamma1 predominant. Furthermore, their tissue-specific distribution suggested that the AMP-activated protein kinase-alpha1 catalytic isoform may contribute, via amplification of the metabolic signal, to the pulmonary selectivity required for hypoxic pulmonary vasoconstriction. Immunocytochemistry showed AMP-activated protein kinase-alpha1 to be located throughout the cytoplasm of pulmonary arterial myocytes. In contrast, it was targeted to the plasma membrane in carotid body glomus cells. Consistent with these observations and the effects of hypoxia, stimulation of AMP-activated protein kinase by phenformin or 5-aminoimidazole-4-carboxamide-riboside elicited discrete Ca2+ signaling mechanisms in each cell type, namely cyclic ADP-ribose-dependent Ca2+ mobilization from the sarcoplasmic reticulum via ryanodine receptors in pulmonary arterial myocytes and transmembrane Ca2+ influx into carotid body glomus cells. Thus, metabolic sensing by AMP-activated protein kinase may mediate chemotransduction by hypoxia.
特殊的氧感应细胞对氧供应调节的阈值特别低，其功能是将动脉血氧分压维持在生理限度内。例如，低氧性肺血管收缩可优化肺内的通气-灌注匹配，而颈动脉体兴奋会引发纠正性的心肺反射。人们普遍认为，相对轻度的缺氧会抑制氧感应细胞中的线粒体氧化磷酸化，从而在一定程度上介导细胞激活。然而，这一过程与钙信号机制耦合的机制仍然不清楚，对先前假说的研究产生了相互矛盾的数据，未能使该领域达成共识。我们提出，细胞内AMP/ATP比值的升高会激活AMP激活的蛋白激酶，从而在氧感应细胞中引发钙信号。免疫共沉淀法在肺动脉肌细胞中鉴定出三种可能的AMP激活的蛋白激酶亚基异构体组合，其中α1β2γ1占主导。此外，它们的组织特异性分布表明，AMP激活的蛋白激酶-α1催化异构体可能通过放大代谢信号，对低氧性肺血管收缩所需的肺选择性起作用。免疫细胞化学显示，AMP激活的蛋白激酶-α1位于肺动脉肌细胞的整个细胞质中。相比之下，它定位于颈动脉体球细胞的质膜上。与这些观察结果以及缺氧的影响一致，苯乙双胍或5-氨基咪唑-4-甲酰胺核苷对AMP激活的蛋白激酶的刺激在每种细胞类型中引发了离散的钙信号机制，即通过肺动脉肌细胞中的ryanodine受体从肌浆网中动员依赖环ADP核糖的钙，以及跨膜钙流入颈动脉体球细胞。因此，AMP激活的蛋白激酶介导的代谢感应可能介导缺氧的化学转导。
