The cellular and molecular basis of bitter tastant-induced bronchodilation.
The cellular and molecular basis of bitter tastant-induced bronchodilation.
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DOI：
10.1371/journal.pbio.1001501
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发表时间：
2013
期刊：
影响因子：
9.8
通讯作者：
ZhuGe R
中科院分区：
文献类型：
--
作者：
Zhang CH;Lifshitz LM;Uy KF;Ikebe M;Fogarty KE;ZhuGe R
苦味促味剂可以激活收缩的平滑肌细胞上的苦味受体，从而抑制L型钙通道并诱导支气管扩张。支气管扩张剂是治疗气道阻塞性疾病的标准药物，β2肾上腺素能受体激动剂自发现以来一直是最常用的支气管扩张剂。值得注意的是，气道平滑肌（ASM）中G蛋白偶联苦味受体（TAS 2 R）的激活在体外和体内引起比β2激动剂更强的支气管扩张作用，这意味着可以开发新的更好的支气管扩张剂。实现这一潜力的关键一步是了解这种支气管扩张的机制，这仍然不明确。一个有影响力的假说认为，苦味促味剂产生本地化的Ca 2+信号，如在培养的ASM细胞中所揭示的，激活大电导Ca 2+激活的K+通道，这反过来又使膜过度膨胀，导致松弛。在这里，我们报告说，在小鼠原代ASM细胞苦味剂既不引起本地化的Ca 2+事件，也不改变自发的局部Ca 2+瞬变。有趣的是，它们增加整体细胞内[Ca 2 +]i，尽管比支气管收缩剂低得多。我们表明，这些钙离子在细胞中的变化在休息是介导的激活经典苦味信号级联（即，TAS 2 R-味觉蛋白-磷脂酶Cβ [PLCβ]-肌醇1，4，5-三磷酸受体[IP 3R]），并且不足以影响气道收缩性。但是TAS 2 Rs的激活完全逆转了由支气管收缩剂诱导的[Ca 2 +]i的增加，并且[Ca 2 +]i的这种降低对于苦味素诱导的ASM细胞松弛是必要的。我们进一步表明，苦味促味剂抑制L-型电压依赖性钙通道（VDCCs），导致[Ca 2 +]i逆转，并且这种抑制可以被百日咳毒素和G-蛋白βγ亚基抑制剂阻止，但不能被PLCβ和IP 3R阻断剂阻止。总之，我们认为TAS 2 R刺激通过Gβγ激活两个相反的Ca 2+信号通路，以增加静息时的[Ca 2 +]i，同时阻断激活的L型VDCC，以诱导收缩的ASM的支气管扩张。我们提出，有效的促味剂支气管扩张剂引起的[Ca 2 +]i的大幅下降提供了一种有效的基于细胞的筛选方法，用于从数千种可用的促苦味剂中鉴定有效的扩张剂。苦味受体（TAS 2 Rs），一个长期以来被认为只在舌头上的味蕾中表达的G蛋白偶联受体家族，最近在气道中被检测到。苦味物质可以激活气道平滑肌中的TAS 2 R，从而比最常用的支气管扩张剂β2肾上腺素能受体激动剂产生更大的支气管扩张作用。然而，这种支气管扩张的机制仍然难以捉摸。在这里，我们表明，在休息的初级气道平滑肌细胞，苦味促味剂激活TAS 2 R依赖的信号通路，导致细胞内钙水平的增加，尽管水平远低于支气管收缩剂产生的。然而，在支气管收缩的细胞中，促苦味剂逆转了支气管收缩剂诱导的钙水平增加，这导致平滑肌细胞松弛。我们发现这种逆转是由于L型钙通道的抑制。我们的研究结果表明，在正常条件下，苦味促味剂可以激活TAS 2 R，适度增加钙水平，但当平滑肌细胞收缩时，它们可以阻断L型钙通道，诱导支气管扩张。我们假设这种新的机制可以在其他表达TAS 2 Rs的口外细胞中发挥作用。
Bitter tastants can activate bitter taste receptors on constricted smooth muscle cells to inhibit L-type calcium channels and induce bronchodilation. Bronchodilators are a standard medicine for treating airway obstructive diseases, and β2 adrenergic receptor agonists have been the most commonly used bronchodilators since their discovery. Strikingly, activation of G-protein-coupled bitter taste receptors (TAS2Rs) in airway smooth muscle (ASM) causes a stronger bronchodilation in vitro and in vivo than β2 agonists, implying that new and better bronchodilators could be developed. A critical step towards realizing this potential is to understand the mechanisms underlying this bronchodilation, which remain ill-defined. An influential hypothesis argues that bitter tastants generate localized Ca2+ signals, as revealed in cultured ASM cells, to activate large-conductance Ca2+-activated K+ channels, which in turn hyperpolarize the membrane, leading to relaxation. Here we report that in mouse primary ASM cells bitter tastants neither evoke localized Ca2+ events nor alter spontaneous local Ca2+ transients. Interestingly, they increase global intracellular [Ca2+]i, although to a much lower level than bronchoconstrictors. We show that these Ca2+ changes in cells at rest are mediated via activation of the canonical bitter taste signaling cascade (i.e., TAS2R-gustducin-phospholipase Cβ [PLCβ]- inositol 1,4,5-triphosphate receptor [IP3R]), and are not sufficient to impact airway contractility. But activation of TAS2Rs fully reverses the increase in [Ca2+]i induced by bronchoconstrictors, and this lowering of the [Ca2+]i is necessary for bitter tastant-induced ASM cell relaxation. We further show that bitter tastants inhibit L-type voltage-dependent Ca2+ channels (VDCCs), resulting in reversal in [Ca2+]i, and this inhibition can be prevented by pertussis toxin and G-protein βγ subunit inhibitors, but not by the blockers of PLCβ and IP3R. Together, we suggest that TAS2R stimulation activates two opposing Ca2+ signaling pathways via Gβγ to increase [Ca2+]i at rest while blocking activated L-type VDCCs to induce bronchodilation of contracted ASM. We propose that the large decrease in [Ca2+]i caused by effective tastant bronchodilators provides an efficient cell-based screening method for identifying potent dilators from among the many thousands of available bitter tastants. Bitter taste receptors (TAS2Rs), a G-protein-coupled receptor family long thought to be solely expressed in taste buds on the tongue, have recently been detected in airways. Bitter substances can activate TAS2Rs in airway smooth muscle to cause greater bronchodilation than β2 adrenergic receptor agonists, the most commonly used bronchodilators. However, the mechanisms underlying this bronchodilation remain elusive. Here we show that, in resting primary airway smooth muscle cells, bitter tastants activate a TAS2R-dependent signaling pathway that results in an increase in intracellular calcium levels, albeit to a level much lower than that produced by bronchoconstrictors. In bronchoconstricted cells, however, bitter tastants reverse the bronchoconstrictor-induced increase in calcium levels, which leads to the relaxation of smooth muscle cells. We find that this reversal is due to inhibition of L-type calcium channels. Our results suggest that under normal conditions, bitter tastants can activate TAS2Rs to modestly increase calcium levels, but that when smooth muscle cells are constricted, they can block L-type calcium channels to induce bronchodilation. We postulate that this novel mechanism could operate in other extraoral cells expressing TAS2Rs.
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气道平滑肌上的苦味受体通过局部钙信号传导和反向阻塞来支气管扩张。
影响因子：
82.9
作者：
通讯作者：
--
影响因子：
14.2
作者：
AHMED, T;DBROT, J;ABRAHAM, W
通讯作者：
ABRAHAM, W
影响因子：
2.9
作者：
Dehkordi, Ozra;Rose, Jed E.;Jayam-Trouth, Annapurni
通讯作者：
Jayam-Trouth, Annapurni
DOI：
10.1513/pats.201102-016rm
发表时间：
2011-08-01
期刊：
Proceedings of the American Thoracic Society
影响因子：
--
作者：
Han, Meilan K;Martinez, Fernando J
通讯作者：
Martinez, Fernando J
DOI：
10.1164/ajrccm/136.5.1179
发表时间：
1987-11-01
期刊：
AMERICAN REVIEW OF RESPIRATORY DISEASE
影响因子：
--
作者：
HARMAN, E;HILL, M;HENDELES, L
通讯作者：
HENDELES, L