Tribe R M, Borin M L, Blaustein M P
Department of Physiology, University of Maryland School of Medicine, Baltimore 21201.
Proc Natl Acad Sci U S A. 1994 Jun 21;91(13):5908-12. doi: 10.1073/pnas.91.13.5908.
Sarcoplasmic reticulum Ca2+ in vascular smooth muscle may be separated into at least two types of Ca2+ stores, one releasable by inositol 1,4,5-trisphosphate and the other releasable by caffeine and ryanodine. We employed digital imaging with fura-2 to study the effects of thapsigargin (which blocks Ca2+ sequestration in the inositol trisphosphate-sensitive store) and caffeine on the cytosolic free Ca2+ concentration ([Ca2+]cyt) in cultured arterial myocytes. These agents increased [Ca2+]cyt by depleting different Ca2+ stores in the absence of extracellular Ca2+. Moreover, Ca2+ could be transferred between the two stores, as prior application of caffeine, which alone evoked little or no rise in [Ca2+]cyt, significantly augmented the response to thapsigargin. Conversely, a substantial caffeine-induced rise in [Ca2+]cyt was observed only after the ability of the thapsigargin-sensitive Ca2+ store to sequester Ca2+ was inhibited. This suggests that the caffeine-sensitive store may have a thapsigargin-insensitive Ca(2+)-sequestration mechanism. To complement these fura-2 experiments, chlortetracycline was used to visualize the Ca2+ stores directly. The latter studies revealed spatial differences in the location of the thapsigargin-sensitive and caffeine-sensitive Ca2+ stores (measured as thapsigargin-sensitive and caffeine-sensitive chlortetracycline fluorescence). Thus, these two types of stores appear to be both functionally and spatially distinct.
血管平滑肌中的肌浆网Ca2+可分为至少两种类型的Ca2+储存库，一种可被肌醇1,4,5 -三磷酸释放，另一种可被咖啡因和ryanodine释放。我们采用fura - 2数字成像技术研究了毒胡萝卜素（它阻断肌醇三磷酸敏感储存库中的Ca2+螯合）和咖啡因对培养的动脉肌细胞胞质游离Ca2+浓度（[Ca2+]cyt）的影响。在没有细胞外Ca2+的情况下，这些试剂通过耗尽不同的Ca2+储存库来增加[Ca2+]cyt。此外，Ca2+可以在两个储存库之间转移，因为预先应用咖啡因（单独使用时几乎不会引起[Ca2+]cyt升高）可显著增强对毒胡萝卜素的反应。相反，只有在毒胡萝卜素敏感的Ca2+储存库螯合Ca2+的能力受到抑制后，才观察到咖啡因引起的[Ca2+]cyt显著升高。这表明咖啡因敏感的储存库可能具有对毒胡萝卜素不敏感的Ca(2+)螯合机制。为补充这些fura - 2实验，使用金霉素直接观察Ca2+储存库。后者的研究揭示了毒胡萝卜素敏感和咖啡因敏感的Ca2+储存库位置上的空间差异（以毒胡萝卜素敏感和咖啡因敏感的金霉素荧光来衡量）。因此，这两种类型的储存库在功能和空间上似乎都是不同的。
