Contribution of the endoplasmic reticulum to the glucose-induced [Ca2+]c response in mouse pancreatic islets
Contribution of the endoplasmic reticulum to the glucose-induced [Ca2+]c response in mouse pancreatic islets
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DOI：
10.1152/ajpendo.00347.2001
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发表时间：
2002-05-01
影响因子：
5.1
通讯作者：
Gilon, P
中科院分区：
文献类型：
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作者：
Arredouani, A;Henquin, JC;Gilon, P
Thapsigargin（TG）是内质网（ER）摄取Ca 2+的阻断剂，用于评价细胞器对小鼠胰腺β细胞中由重复Ca 2+内流诱导的胞质Ca 2+浓度振荡（[Ca 2 +]（c））的贡献。由于TG去极化的质膜在单独的葡萄糖的存在下，细胞外K+交替在10和30 mM之间的二氮嗪的存在下施加膜电位（MP）振荡。在对照胰岛中，模拟由10 mM葡萄糖引起的规则MP振荡的K+脉冲诱导[Ca2+]（c）振荡，其最低点保持高于基础[Ca2+]（c）。增加脉冲的去极化相位，同时保持其频率恒定（以模拟葡萄糖浓度进一步升高对MP的影响），导致[Ca2+]（c）振荡的最低点上移，这是通过提高细胞外Ca2+（以增加Ca2+内流）而不改变脉冲方案来再现的。在TG预处理的胰岛中，施加的[Ca 2 +]（c）振荡的幅度比对照胰岛大得多，并且发生在基础水平上。在间歇性去极化过程中，对照组胰岛显示混合的[Ca 2 +]（c）振荡，其特征在于在缓慢的振荡之上快速振荡的总和，而在TG预处理的胰岛中没有观察到快速振荡的渐进性总和。总之，胰腺β细胞中ER的缓冲能力限制了[Ca2+]（c）振荡的幅度，并可以解释振荡之间的最低点如何在规则振荡期间保持在基线以上，或在混合[Ca2+]（c）振荡期间逐渐增加，这是葡萄糖刺激期间观察到的两种类型的反应。
Thapsigargin (TG), a blocker of Ca2+ uptake by the endoplasmic reticulum (ER), was used to evaluate the contribution of the organelle to the oscillations of cytosolic Ca2+ concentration ([Ca2+](c)) induced by repetitive Ca2+ influx in mouse pancreatic beta-cells. Because TG depolarized the plasma membrane in the presence of glucose alone, extracellular K+ was alternated between 10 and 30 mM in the presence of diazoxide to impose membrane potential (MP) oscillations. In control islets, pulses of K+, mimicking regular MP oscillations elicited by 10 mM glucose, induced [Ca2+](c) oscillations whose nadir remained higher than basal [Ca2+](c). Increasing the depolarization phase of the pulses while keeping their frequency constant (to mimic the effects of a further rise of the glucose concentration on MP) caused an upward shift of the nadir of [Ca2+](c) oscillations that was reproduced by raising extracellular Ca2+ (to increase Ca2+ influx) without changing the pulse protocol. In TG-pretreated islets, the imposed [Ca2+](c) oscillations were of much larger amplitude than in control islets and occurred on basal levels. During intermittent trains of depolarizations, control islets displayed mixed [Ca2+](c) oscillations characterized by a summation of fast oscillations on top of slow ones, whereas no progressive summation of the fast oscillations was observed in TG-pretreated islets. In conclusion, the buffering capacity of the ER in pancreatic beta-cells limits the amplitude of [Ca2+](c) oscillations and may explain how the nadir between oscillations remains above baseline during regular oscillations or gradually increases during mixed [Ca2+](c) oscillations, two types of response observed during glucose stimulation.