Foskett J K, Wong D
Division of Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada.
Am J Physiol. 1992 Mar;262(3 Pt 1):C656-63. doi: 10.1152/ajpcell.1992.262.3.C656.
Previous studies have demonstrated in single rat parotid acinar cells that the microsomal Ca(2+)-ATPase inhibitor thapsigargin mobilizes Ca2+ specifically from the inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store, activates plasma membrane Ca2+ permeability, and induces intracellular Ca2+ concentration ([Ca2+]i) oscillations that are quite similar to those activated by carbachol. Nevertheless, the IP3-sensitive Ca2+ store remains continuously depleted during thapsigargin-induced oscillations, indicating that this pool is not involved in the oscillation mechanism. To determine the specificity of thapsigargin's effects, in the present study we have examined the effects on [Ca2+]i in single rat parotid acinar cells of two other microsomal Ca(2+)-ATPase inhibitors, cyclopiazonic acid (CPA) and 2,5-di-tert-butyl-1,4-benzohydroquinone (BHQ), and compared them with the effects of thapsigargin in the same cells. Our results demonstrate that thapsigargin, CPA, and BHQ all similarly deplete the IP3-sensitive Ca2+ store specifically, activate plasma membrane Ca2+ influx, and induce [Ca2+]i oscillations, strongly suggesting that these agents have a specific inhibitory action on microsomal Ca(2+)-ATPase activity. BHQ, in addition, inhibits plasma membrane Ca2+ influx. The data lend strong support to a model in which the state of Ca2+ filling of the IP3-sensitive store regulates plasma membrane Ca2+ influx. These results suggest either that a Ca2+ pump is involved which is insensitive to structurally dissimilar inhibitors or that a Ca2+ pump is not involved in refilling of the Ca2+ pool involved in [Ca2+]i oscillations in these cells.
先前的研究已在单个大鼠腮腺腺泡细胞中证实，微粒体Ca(2+)-ATP酶抑制剂毒胡萝卜素能特异性地从肌醇1,4,5-三磷酸（IP3）敏感的Ca2+储存库中释放Ca2+，激活质膜Ca2+通透性，并诱导细胞内Ca2+浓度（[Ca2+]i）振荡，这些振荡与由卡巴胆碱激活的振荡非常相似。然而，在毒胡萝卜素诱导的振荡过程中，IP3敏感的Ca2+储存库持续耗尽，这表明该池不参与振荡机制。为了确定毒胡萝卜素作用的特异性，在本研究中，我们检测了另外两种微粒体Ca(2+)-ATP酶抑制剂环匹阿尼酸（CPA）和2,5-二叔丁基-1,4-苯二酚（BHQ）对单个大鼠腮腺腺泡细胞[Ca2+]i的影响，并将它们与毒胡萝卜素在相同细胞中的作用进行了比较。我们的结果表明，毒胡萝卜素、CPA和BHQ都同样能特异性地耗尽IP3敏感的Ca2+储存库，激活质膜Ca2+内流，并诱导[Ca2+]i振荡，这强烈表明这些药物对微粒体Ca(2+)-ATP酶活性具有特异性抑制作用。此外，BHQ还抑制质膜Ca2+内流。这些数据有力地支持了一个模型，即IP3敏感储存库的Ca2+填充状态调节质膜Ca2+内流。这些结果表明，要么存在一种对结构不同的抑制剂不敏感的Ca2+泵参与其中，要么不存在Ca2+泵参与这些细胞中[Ca2+]i振荡所涉及的Ca2+池的再填充。
