Connexin hemichannel-mediated CO2-dependent release of ATP in the medulla oblongata contributes to central respiratory chemosensitivity
Connexin hemichannel-mediated CO2-dependent release of ATP in the medulla oblongata contributes to central respiratory chemosensitivity
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DOI：
10.1113/jphysiol.2010.192088
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发表时间：
2010-10-15
影响因子：
5.5
通讯作者：
Dale, Nicholas
中科院分区：
文献类型：
--
作者：
Huckstepp, Robert T. R.;Bihi, Rachid Id;Dale, Nicholas
动脉P-CO2是呼吸的主要决定因素，由位于脑干中的化学传感器检测。这些对于维持血液和大脑中CO2的生理水平很重要，但大脑感知CO2的机制仍然存在争议。由于脑干腹侧表面的ATP释放与高碳酸血症时通气的适应性变化有因果关系，我们研究了含有延髓腹侧表面的切片中CO2依赖性ATP释放的机制。我们发现，CO2依赖的ATP释放发生在细胞外酸化的情况下，并与P-CO2的水平直接相关。ATP的释放不依赖于细胞外Ca 2+，可能通过缝隙连接半通道的开放而发生。由于作用于连接蛋白通道的药物阻断了这种释放，但对泛连接蛋白-1具有选择性的化合物没有影响，因此我们得出结论，连接蛋白半通道参与了CO2依赖性ATP释放。我们已经使用分子，遗传和免疫细胞化学技术证明，在延髓连接蛋白26（Cx 26）的腹侧表面附近的优先表达。软脑膜，软膜下星形胶质细胞和星形胶质细胞鞘穿透血管在腹侧表面的髓质可以加载染料在CO2依赖性的方式，表明门控的半通道参与ATP的释放。这种CO2依赖性染料负载的分布密切反映了Cx 26的表达，并与胶质细胞酸性蛋白（GFAP）阳性细胞共定位。在体内，具有Cx 26选择性的阻断剂减少高碳酸血症诱发的ATP释放和随后的呼吸适应性增强。因此，我们认为，Cx 26介导的释放ATP响应于P-CO2的变化是一个重要的机制，有助于中央呼吸化疗敏感性。
Arterial P-CO2, a major determinant of breathing, is detected by chemosensors located in the brainstem. These are important for maintaining physiological levels of CO2 in the blood and brain, yet the mechanisms by which the brain senses CO2 remain controversial. As ATP release at the ventral surface of the brainstem has been causally linked to the adaptive changes in ventilation in response to hypercapnia, we have studied the mechanisms of CO2-dependent ATP release in slices containing the ventral surface of the medulla oblongata. We found that CO2-dependent ATP release occurs in the absence of extracellular acidification and correlates directly with the level of P-CO2. ATP release is independent of extracellular Ca2+ and may occur via the opening of a gap junction hemichannel. As agents that act on connexin channels block this release, but compounds selective for pannexin-1 have no effect, we conclude that a connexin hemichannel is involved in CO2-dependent ATP release. We have used molecular, genetic and immunocytochemical techniques to demonstrate that in the medulla oblongata connexin 26 (Cx26) is preferentially expressed near the ventral surface. The leptomeninges, subpial astrocytes and astrocytes ensheathing penetrating blood vessels at the ventral surface of the medulla can be loaded with dye in a CO2-dependent manner, suggesting that gating of a hemichannel is involved in ATP release. This distribution of CO2-dependent dye loading closely mirrors that of Cx26 expression and colocalizes to glial fibrillary acidic protein (GFAP)-positive cells. In vivo, blockers with selectivity for Cx26 reduce hypercapnia-evoked ATP release and the consequent adaptive enhancement of breathing. We therefore propose that Cx26-mediated release of ATP in response to changes in P-CO2 is an important mechanism contributing to central respiratory chemosensitivity.