Wu S N, Yu H S, Seyama Y
Department of Physiology, Kaohsiung Medical College, Taiwan.
J Biochem. 1995 Feb;117(2):309-14. doi: 10.1093/jb/117.2.309.
The change of cytosolic Ca2+ concentration ([Ca2+]i) caused by vasopressin was examined in indo-1-loaded A7r5 smooth muscle cells by use of the high-performance laser cytometer and ratiometric fluorescence method. Vasopressin (100 nM) caused an initial rapid rise and a delayed increase in [Ca2+]i (n = 6). However, in the presence of tetraethylammonium chloride (10 mM), vasopressin consistently triggered sustained Ca2+ oscillations which were preceded by a large peak of [Ca2+]i. The latency for the development of this huge increase in [Ca2+]i prior to the occurrence of sustained Ca2+ oscillations was always the same. The frequency and amplitude of this type of Ca2+ oscillation varied depending upon the extracellular Ca2+ concentration. Ca(2+)-free solution did not completely suppress the sustained Ca2+ oscillations, but caffeine (20 mM) effectively abolished them. The present findings indicate that in A7r5 smooth muscle cells, the sustained Ca2+ oscillations triggered by vasopressin in the presence of tetraethylammonium chloride were mainly due to Ca2+ release from IP3-sensitive Ca2+ stores and Ca2+ influx from extracellular space, and did not require the pacemaker activity derived from the surface membrane. Moreover, the vasopressin-induced change in [Ca2+]i appeared to be linked to pertussis toxin-insensitive GTP-binding protein(s).
利用高性能激光细胞仪和比率荧光法，在负载indo-1的A7r5平滑肌细胞中检测了血管加压素引起的胞质Ca2+浓度（[Ca2+]i）变化。血管加压素（100 nM）引起[Ca2+]i先迅速升高，随后延迟增加（n = 6）。然而，在存在四乙铵氯化物（10 mM）的情况下，血管加压素持续引发持续性Ca2+振荡，在振荡之前[Ca2+]i会出现一个大峰值。在持续性Ca2+振荡出现之前，[Ca2+]i出现这种大幅增加的延迟时间总是相同的。这种类型的Ca2+振荡的频率和幅度因细胞外Ca2+浓度而异。无Ca2+溶液不能完全抑制持续性Ca2+振荡，但咖啡因（20 mM）能有效消除它们。目前的研究结果表明，在A7r5平滑肌细胞中，在四乙铵氯化物存在的情况下，血管加压素引发的持续性Ca2+振荡主要是由于IP3敏感的Ca2+储存库释放Ca2+以及细胞外空间Ca2+内流，并不需要源自表面膜的起搏器活性。此外，血管加压素诱导的[Ca2+]i变化似乎与百日咳毒素不敏感的GTP结合蛋白有关。
