Involvement of Ca2+ mobilization in tachyphylaxis to β-adrenergic receptors in trachealis
Involvement of Ca2+ mobilization in tachyphylaxis to β-adrenergic receptors in trachealis
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DOI：
10.1165/rcmb.2002-0197oc
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发表时间：
2003-09-01
影响因子：
6.4
通讯作者：
Kotlikoff, MI
中科院分区：
文献类型：
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作者：
Kume, H;Ishikawa, T;Kotlikoff, MI
我们研究了气管平滑肌对β-肾上腺素能受体激动剂(β-激动剂)发生快速反应的机制。用Fura-2负载的豚鼠气管同时测定等长张力和细胞内钙离子浓度([Ca~(2+)](I))，结果表明，异丙肾上腺素(ISO)对乙酰甲胆碱引起的张力和[Ca~(2+)]升高有明显的抑制作用，每隔15分钟重复暴露ISO一次，表现出明显的快速反应。同样地，1um ISO对单个细胞膜上钙激活K+(K-Ca)通道的激活作用在细胞外反复作用于单个猪气管平滑肌细胞后逐渐减弱。用异搏定分别拮抗电压依赖性呼唤通道(VDCC)，可阻止β-肾上腺素能受体/K-Ca通道刺激性偶联和松弛反应的脱敏，提示VDCC中的钙离子内流与β-肾上腺素能脱敏有惊人的关系。反之，10U/mlProtein Kinase A反复暴露于内向外贴片并未导致通道激活的脱敏，而重复暴露10um Forsklin可轻度增强Forsklin对张力和乙酰甲胆碱所致的[Ca~(2+)](I)的抑制作用，提示其脱敏机制是由β-肾上腺素能受体/G蛋白复合体介导的。这些结果表明，钾-钙通道上的β-肾上腺素能受体的解偶联增强了通过VDCC的钙动员，并刺激了快速反应。
We examined the mechanisms underlying tachyphylaxis to beta-adrenergic receptor agonists (beta-agonists) in tracheal smooth muscle. Simultaneous measurements of isometric tension and intracellular Ca2+ concentration ([Ca2+](i)) using fura-2-loaded guinea pig tracheas showed that the inhibitory effects of isoproterenol (ISO) on tension and increases in [Ca2+], induced by methacholine exhibited marked tachyphylaxis with repeated exposure to ISO at intervals of 15 min. Similarly, the activation of single Ca2+-activated K+ (K-Ca) channels in on-cell patches by 1 muM ISO was gradually attenuated after repeated extracellular application of ISO to single smooth cells of porcine tracheas. Desensitization of beta-adrenergic receptor/K-Ca channel stimulatory coupling and relaxation responses was prevented by separately antagonizing the voltage-dependent Call channel (VDCC) with verapamil, suggesting a surprising relationship between Ca2+ influx through VDCC and beta-adrenergic desensitization. Conversely, repeated exposure of 10 U/ml protein kinase A to inside-out patches did not result in desensitization of channel activation, and repeated exposure to 10 muM forskolin modestly augmented the inhibitory effects of forskolin on tension and [Ca2+](i) by methacholine, indicating that the mechanism of desensitization is mediated by the beta-adrenergic receptor/G protein complex. These results indicate that an uncoupling of beta-adrenergic receptor from K-Ca channels augments Ca2+ mobilization through VDCC and stimulates tachyphylaxis.