Glucose Suppression of Glucagon Secretion METABOLIC AND CALCIUM RESPONSES FROM α-CELLS IN INTACT MOUSE PANCREATIC ISLETS
Glucose Suppression of Glucagon Secretion METABOLIC AND CALCIUM RESPONSES FROM α-CELLS IN INTACT MOUSE PANCREATIC ISLETS
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DOI：
10.1074/jbc.m109.069195
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发表时间：
2010-05-07
影响因子：
4.8
通讯作者：
Piston, David W.
中科院分区：
文献类型：
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作者：
Le Marchand, Sylvain J.;Piston, David W.
胰高血糖素在葡萄糖浓度低于4mM时从存在于完整胰岛中的α细胞释放，而较高的葡萄糖水平抑制其分泌。α-细胞分泌活性抑制的潜在机制知之甚少，但已提出两种一般类型的模型如下：葡萄糖直接抑制或郎格罕氏胰岛内非α-细胞的旁分泌抑制。为了鉴定用于分析的α细胞，我们利用表达特异性靶向这些细胞的荧光蛋白的转基因小鼠。从流式分选的α-细胞的纯群体中测量胰高血糖素分泌显示，与其对完整胰岛的作用相反，葡萄糖确实刺激从分离的α-细胞中分泌胰高血糖素。这一观察结果反对葡萄糖直接抑制胰高血糖素分泌，并支持旁分泌抑制模型。通过NAD（P）H自发荧光的双光子激发的细胞代谢成像表明葡萄糖在α细胞中代谢，并且葡萄糖激酶可能是该过程中的限速步骤。完整胰岛中α细胞的钙动力学成像显示，抑制葡萄糖浓度增加了细胞内钙浓度和α细胞钙振荡的频率。候选旁分泌抑制剂的应用导致胰高血糖素分泌减少，但不会降低α细胞钙活性。两者合计，数据表明，抑制发生在α细胞钙信号传导的下游，可能是在囊泡运输或胞吐机制的水平。
Glucagon is released from alpha-cells present in intact pancreatic islets at glucose concentrations below 4 mM, whereas higher glucose levels inhibit its secretion. The mechanisms underlying the suppression of alpha-cell secretory activity are poorly understood, but two general types of models have been proposed as follows: direct inhibition by glucose or paracrine inhibition from non-alpha-cells within the islet of Langerhans. To identify alpha-cells for analysis, we utilized transgenic mice expressing fluorescent proteins targeted specifically to these cells. Measurements of glucagon secretion from pure populations of flow-sorted alpha-cells show that contrary to its effect on intact islets, glucose does stimulate glucagon secretion from isolated alpha-cells. This observation argues against a direct inhibition of glucagon secretion by glucose and supports the paracrine inhibition model. Imaging of cellular metabolism by two-photon excitation of NAD(P) H autofluorescence indicates that glucose is metabolized in alpha-cells and that glucokinase is the likely rate-limiting step in this process. Imaging calcium dynamics of alpha-cells in intact islets reveals that inhibiting concentrations of glucose increase the intracellular calcium concentration and the frequency of alpha-cell calcium oscillations. Application of candidate paracrine inhibitors leads to reduced glucagon secretion but did not decrease the alpha-cell calcium activity. Taken together, the data suggest that suppression occurs downstream from alpha-cell calcium signaling, presumably at the level of vesicle trafficking or exocytotic machinery.