Longo E A, Tornheim K, Deeney J T, Varnum B A, Tillotson D, Prentki M, Corkey B E
Evans Department of Medicine, Boston University School of Medicine, Massachusetts 02118.
J Biol Chem. 1991 May 15;266(14):9314-9.
Insulin secretion in the intact organism, and by the perfused pancreas and groups of isolated perifused islets, is pulsatile. We have proposed a metabolic model of glucose-induced insulin secretion in which oscillations in the ATP/ADP ratio drive alterations in metabolic and electrical events that lead to insulin release. A key prediction of our model is that metabolically driven Ca2+ oscillations will also occur. Using the fluorescent Ca2+ probe, fura 2, digital image analysis, and sensitive O2 electrodes, we investigated cytosolic free Ca2+ responses and O2 consumption in perifused rat islets that had been maintained in culture for 1-4 days. We found that elevated ambient glucose increased the average cytosolic free Ca2+ level, the ATP/ADP ratio, and oxygen consumption, as previously found in freshly isolated islets. Oscillatory patterns were obtained for Ca2+, O2 consumption, and insulin secretion in the presence of 10 and 20 mM glucose. Very low amplitude oscillations in cytosolic free Ca2+ were observed at 3 mM nonstimulatory glucose levels. Evaluation of the Ca2+ responses of a large series of individual islets, monitored by digital image analysis and perifused at both 3 and 10 mM glucose, indicated that the rise in glucose concentration caused more than a doubling of the average cytosolic free Ca2+ value and a 4-fold increase in the amplitude of the oscillations with little change in period. The pattern of Ca2+ change within the islets was consistent with recruitment of responding cells. The coexistence of oscillations with similar periods in insulin secretion, oxygen consumption, and cytosolic free Ca2+ is consistent with the model of metabolically driven pulsatile insulin secretion.
在完整机体中，以及通过灌注胰腺和分离的胰岛群进行灌注时，胰岛素分泌是呈脉冲式的。我们提出了一种葡萄糖诱导胰岛素分泌的代谢模型，其中ATP/ADP比值的振荡驱动代谢和电活动的改变，进而导致胰岛素释放。我们模型的一个关键预测是，代谢驱动的Ca2+振荡也会发生。利用荧光Ca2+探针fura 2、数字图像分析和灵敏的O2电极，我们研究了培养1 - 4天的灌注大鼠胰岛中的胞质游离Ca2+反应和O2消耗。我们发现，环境葡萄糖升高会增加平均胞质游离Ca2+水平、ATP/ADP比值和氧消耗，这与之前在新鲜分离的胰岛中发现的情况一致。在10和20 mM葡萄糖存在的情况下，获得了Ca2+、O2消耗和胰岛素分泌的振荡模式。在3 mM非刺激葡萄糖水平下，观察到胞质游离Ca2+的振荡幅度非常低。通过数字图像分析监测并在3和10 mM葡萄糖下进行灌注的大量单个胰岛的Ca2+反应评估表明，葡萄糖浓度的升高导致平均胞质游离Ca2+值增加了一倍多，振荡幅度增加了4倍，而周期变化很小。胰岛内Ca2+变化的模式与反应细胞的募集一致。胰岛素分泌、氧消耗和胞质游离Ca2+中具有相似周期的振荡共存与代谢驱动的脉冲式胰岛素分泌模型一致。
