Miki H, Maercklein P B, Fitzpatrick L A
Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
Endocrinology. 1995 Jul;136(7):2954-9. doi: 10.1210/endo.136.7.7789320.
PTH secretion is tightly regulated by extracellular calcium ([Ca2+]e) and in turn regulates calcium homeostasis through its action on target tissues. We investigated the mechanism and physiological significance of intracellular calcium ([Ca2+]i) levels in relation to the secretion of PTH in single bovine parathyroid cells. [Ca2+]i was recorded using digital imaging microscopy, and secretion of PTH was correlated in the same cell using the reverse hemolytic plaque assay. In individual parathyroid cells, oscillations of [Ca2+]i were present in response to specific stimuli. Like secretory activity, response to [Ca2+]e concentrations was heterogeneous. Oscillations of [Ca2+]i occurred spontaneously in 22% of cells at inhibitory concentrations of [Ca2+]e. Oscillations were present only in high [Ca2+]e (> or = 1.8 mM) and not noted at lower concentrations of [Ca2+]e. The interval and amplitude of [Ca2+]i oscillations were 42 +/- 2 sec, and 20 +/- 1 nM (mean +/- SE), respectively. Oscillations were rapidly abolished when [Ca2+]e was removed by EGTA, and this effect was reversible. Addition of Mg2+ or polycationic antibiotics such as neomycin resulted in an [Ca2+]i spike, but oscillations were absent. Lanthanum, which blocks Ca2+ influx through calcium channels in various cells, rarely caused oscillations even in the presence of high concentrations of [Ca2+]e. To test the role of cAMP in [Ca2+]i oscillations, we added the beta-agonist isoproterenol. The addition of isoproterenol, however, did not cause oscillations. The number of cells that released PTH was significantly lower in cells with oscillations compared with cells without oscillations. We suggest that spontaneous [Ca2+]i oscillations are due to the influx of [Ca2+]e through ion channels rather than release from [Ca2+]i stores and may be a specific intracellular signal associated with inhibition of PTH secretion.
甲状旁腺激素（PTH）的分泌受细胞外钙（[Ca2+]e）严格调控，反过来它又通过作用于靶组织来调节钙稳态。我们研究了单个牛甲状旁腺细胞内钙（[Ca2+]i）水平与PTH分泌相关的机制及生理意义。使用数字成像显微镜记录[Ca2+]i，并在同一细胞中使用反向溶血空斑试验将PTH的分泌与之关联。在单个甲状旁腺细胞中，[Ca2+]i会因特定刺激而出现振荡。与分泌活性一样，对[Ca2+]e浓度的反应也是异质性的。在抑制性[Ca2+]e浓度下，22%的细胞中[Ca2+]i会自发振荡。振荡仅出现在高[Ca2+]e（≥1.8 mM）时，在较低[Ca2+]e浓度下未观察到。[Ca2+]i振荡的间隔和幅度分别为42±2秒和20±1 nM（平均值±标准误）。当用乙二醇双四乙酸（EGTA）去除[Ca2+]e时，振荡迅速消失，且这种效应是可逆的。添加镁离子（Mg2+）或多阳离子抗生素如新霉素会导致[Ca2+]i峰值，但无振荡。镧可阻断各种细胞中通过钙通道的钙内流，即使在高浓度[Ca2+]e存在时也很少引起振荡。为了测试环磷酸腺苷（cAMP）在[Ca2+]i振荡中的作用，我们添加了β-激动剂异丙肾上腺素。然而，添加异丙肾上腺素并未引起振荡。与无振荡的细胞相比，有振荡细胞中释放PTH的细胞数量显著减少。我们认为，自发的[Ca2+]i振荡是由于[Ca2+]e通过离子通道内流而非从[Ca2+]i储存库释放所致，并且可能是与PTH分泌抑制相关的一种特定细胞内信号。
