Perez Jose F, Sanderson Michael J
Department of Physiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
J Gen Physiol. 2005 Jun;125(6):535-53. doi: 10.1085/jgp.200409216.
Increased resistance of airways or blood vessels within the lung is associated with asthma or pulmonary hypertension and results from contraction of smooth muscle cells (SMCs). To study the mechanisms regulating these contractions, we developed a mouse lung slice preparation containing bronchioles and arterioles and used phase-contrast and confocal microscopy to correlate the contractile responses with changes in Ca(2+) of the SMCs. The airways are the focus of this study. The agonists, 5-hydroxytrypamine (5-HT) and acetylcholine (ACH) induced a concentration-dependent contraction of the airways. High concentrations of KCl induced twitching of the airway SMCs but had little effect on airway size. 5-HT and ACH induced asynchronous oscillations in Ca(2+) that propagated as Ca(2+) waves within the airway SMCs. The frequency of the Ca(2+) oscillations was dependent on the agonist concentration and correlated with the extent of sustained airway contraction. In the absence of extracellular Ca(2+) or in the presence of Ni(2+), the frequency of the Ca(2+) oscillations declined and the airway relaxed. By contrast, KCl induced low frequency Ca(2+) oscillations that were associated with SMC twitching. Each KCl-induced Ca(2+) oscillation consisted of a large Ca(2+) wave that was preceded by multiple localized Ca(2+) transients. KCl-induced responses were resistant to neurotransmitter blockers but were abolished by Ni(2+) or nifedipine and the absence of extracellular Ca(2+). Caffeine abolished the contractile effects of 5-HT, ACH, and KCl. These results indicate that (a) 5-HT and ACH induce airway SMC contraction by initiating Ca(2+) oscillations, (b) KCl induces Ca(2+) transients and twitching by overloading and releasing Ca(2+) from intracellular stores, (c) a sustained, Ni(2+)-sensitive, influx of Ca(2+) mediates the refilling of stores to maintain Ca(2+) oscillations and, in turn, SMC contraction, and (d) the magnitude of sustained airway SMC contraction is regulated by the frequency of Ca(2+) oscillations.
肺内气道或血管阻力增加与哮喘或肺动脉高压相关，且是由平滑肌细胞（SMC）收缩引起的。为了研究调节这些收缩的机制，我们制备了一种包含细支气管和小动脉的小鼠肺切片标本，并使用相差显微镜和共聚焦显微镜将收缩反应与SMC中[Ca(2+)]i的变化相关联。气道是本研究的重点。激动剂5-羟色胺（5-HT）和乙酰胆碱（ACH）诱导气道产生浓度依赖性收缩。高浓度氯化钾诱导气道SMC抽搐，但对气道大小影响不大。5-HT和ACH诱导[Ca(2+)]i产生异步振荡，该振荡在气道SMC内以Ca(2+)波的形式传播。Ca(2+)振荡的频率取决于激动剂浓度，并与气道持续收缩的程度相关。在无细胞外Ca(2+)或存在Ni(2+)的情况下，Ca(2+)振荡频率下降，气道松弛。相比之下，氯化钾诱导的低频Ca(2+)振荡与SMC抽搐相关。每次氯化钾诱导的Ca(2+)振荡都由一个大的Ca(2+)波组成，该波之前有多个局部Ca(2+)瞬变。氯化钾诱导的反应对神经递质阻滞剂有抗性，但可被Ni(2+)或硝苯地平以及无细胞外Ca(2+)所消除。咖啡因消除了5-HT、ACH和氯化钾的收缩作用。这些结果表明：（a）5-HT和ACH通过引发Ca(2+)振荡诱导气道SMC收缩；（b）氯化钾通过使细胞内钙库超载并释放Ca(2+)诱导Ca(2+)瞬变和抽搐；（c）持续的、对Ni(2+)敏感的Ca(2+)内流介导钙库的再充盈以维持Ca(2+)振荡，进而维持SMC收缩；（d）气道SMC持续收缩的幅度由Ca(2+)振荡的频率调节。
