Glucose-stimulated Single Pancreatic Islets Sustain Increased Cytosolic ATP Levels during Initial Ca2+ Influx and Subsequent Ca2+ Oscillations
Glucose-stimulated Single Pancreatic Islets Sustain Increased Cytosolic ATP Levels during Initial Ca2+ Influx and Subsequent Ca2+ Oscillations
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DOI：
10.1074/jbc.m113.499111
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发表时间：
2014-01-24
影响因子：
4.8
通讯作者：
Imamura, Hiromi
中科院分区：
文献类型：
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作者：
Tanaka, Takashi;Nagashima, Kazuaki;Imamura, Hiromi
在胰岛中，在高葡萄糖条件下，胰岛素分泌通过整个胰岛中Ca 2+水平的同步升高而发生。这种Ca 2+升高有两个阶段：葡萄糖刺激后观察到的快速增加，随后是长时间的振荡。在这些过程中，由葡萄糖产生的细胞内ATP水平的升高被认为抑制ATP敏感性K+通道，导致膜的去极化，这反过来诱导胰岛中的Ca 2+升高。然而，很少有人知道细胞内ATP水平的动态变化及其相关性与Ca 2+水平在胰岛中响应于葡萄糖水平的变化。在这项研究中，一个基因编码的荧光生物传感器ATP和荧光Ca 2+染料，同时监测细胞内ATP和Ca 2+水平的动态，分别在单个孤立的胰岛。我们观察到快速增加的细胞溶质和线粒体ATP水平刺激后，葡萄糖，以及丙酮酸甲酯或亮氨酸/谷氨酰胺。只要高血糖水平持续，高ATP水平就会持续。抑制ATP的产生抑制了初始Ca 2+的增加，这表明增强的能量代谢触发了Ca 2+内流的初始阶段。另一方面，胞浆ATP水平并没有波动显着的Ca 2+水平在随后的振荡阶段。重要的是，在ATP水平显著下降之前，Ca 2+振荡立即停止。这些结果可能解释了食物或葡萄糖摄入如何引起胰岛素分泌，以及由此导致的血糖水平下降如何导致分泌停止。
In pancreatic islets, insulin secretion occurs via synchronous elevation of Ca2+ levels throughout the islets during high glucose conditions. This Ca2+ elevation has two phases: a quick increase, observed after the glucose stimulus, followed by prolonged oscillations. In these processes, the elevation of intracellular ATP levels generated from glucose is assumed to inhibit ATP-sensitive K+ channels, leading to the depolarization of membranes, which in turn induces Ca2+ elevation in the islets. However, little is known about the dynamics of intracellular ATP levels and their correlation with Ca2+ levels in the islets in response to changing glucose levels. In this study, a genetically encoded fluorescent biosensor for ATP and a fluorescent Ca2+ dye were employed to simultaneously monitor the dynamics of intracellular ATP and Ca2+ levels, respectively, inside single isolated islets. We observed rapid increases in cytosolic and mitochondrial ATP levels after stimulation with glucose, as well as with methyl pyruvate or leucine/glutamine. High ATP levels were sustained as long as high glucose levels persisted. Inhibition of ATP production suppressed the initial Ca2+ increase, suggesting that enhanced energy metabolism triggers the initial phase of Ca2+ influx. On the other hand, cytosolic ATP levels did not fluctuate significantly with the Ca2+ level in the subsequent oscillation phases. Importantly, Ca2+ oscillations stopped immediately before ATP levels decreased significantly. These results might explain how food or glucose intake evokes insulin secretion and how the resulting decrease in plasma glucose levels leads to cessation of secretion.