Sims S M, Jiao Y, Zheng Z G
Department of Physiology, University of Western Ontario, London, Canada. sims@physiology. uwo.cn
Am J Physiol. 1996 Aug;271(2 Pt 1):L300-9. doi: 10.1152/ajplung.1996.271.2.L300.
We investigated the effects of acetylcholine (ACh) and histamine on intracellular calcium concentration ([Ca2+]i) and contraction of freshly isolated guinea pig tracheal smooth muscle cells. Previous electrophysiological studies revealed that agonists elicit cation and Cl- currents, but a role for Ca2+ in mediating these effects remains unresolved. Here we characterize agonist-induced changes of [Ca2+]i, using fura 2, and examine the contribution of the sarcoplasmic reticulum (SR) to regulation of [Ca2+]i. We provide evidence that the rise of [Ca2+]i and the contraction elicited by ACh or histamine are largely due to release of Ca2+ from stores. Agonists elicited Ca2+ transients in Ca(2+)-free solution with 0.5 mM ethylene glycol-bis (beta-aminoethyl ether)-N, N, N',N'-tetraacetic acid (EGTA), whereas prolonged exposure to Ca(2+)-free solution diminished the rise of [Ca2+]i. In addition, blockade of SR Ca(2+)-adenosinetriphosphatase (ATPase) by cyclopiazonic acid (CPA) or thapsigargin caused elevation of [Ca2+]i and reduction of ACh-evoked increase of [Ca2+]i. In many cells, [Ca2+]i fell below baseline (undershoot) after ACh or caffeine. CPA abolished this undershoot and reduced the rate of recovery of [Ca2+]i to basal levels. Furthermore, oscillations of [Ca2+]i were elicited in the presence or absence of extracellular Ca2+, and these too were reversibly abolished by CPA. Our results provide evidence that Ca2+ stores play a significant role in agonist-mediated increase of [Ca2+]i in tracheal muscle and that the SR contributes to the restoration of basal Ca2+ levels.
我们研究了乙酰胆碱（ACh）和组胺对新鲜分离的豚鼠气管平滑肌细胞内钙浓度（[Ca2+]i）及收缩的影响。先前的电生理研究表明，激动剂可引发阳离子和Cl-电流，但Ca2+在介导这些效应中的作用仍未明确。在此，我们使用fura 2来表征激动剂诱导的[Ca2+]i变化，并研究肌浆网（SR）对[Ca2+]i调节的贡献。我们提供的证据表明，ACh或组胺引起的[Ca2+]i升高及收缩在很大程度上归因于钙库中Ca2+的释放。激动剂在含0.5 mM乙二醇双（β-氨基乙醚）-N，N，N'，N'-四乙酸（EGTA）的无钙溶液中引发Ca2+瞬变，而长时间暴露于无钙溶液会使[Ca2+]i的升高减弱。此外，环匹阿尼酸（CPA）或毒胡萝卜素对SR Ca2+ - 腺苷三磷酸酶（ATPase）的阻断导致[Ca2+]i升高，并降低ACh引起的[Ca2+]i增加。在许多细胞中，ACh或咖啡因作用后[Ca2+]i降至基线以下（超射）。CPA消除了这种超射，并降低了[Ca2+]i恢复到基础水平的速率。此外，无论有无细胞外Ca2+，均可引发[Ca2+]i振荡，并且这些振荡也可被CPA可逆性消除。我们的结果提供了证据，表明钙库在激动剂介导的气管肌肉[Ca2+]i增加中起重要作用，并且SR有助于基础Ca2+水平的恢复。
