Institute of Pharmacology, Toxicology and Clinical Pharmacy, Technical University of Braunschweig, Mendelssohnstrasse 1, D-38106 Braunschweig, Germany.
Metabolism. 2013 Oct;62(10):1375-86. doi: 10.1016/j.metabol.2013.05.006. Epub 2013 Jun 18.
The β-cell metabolism of glucose and of some other fuels (e.g. α-ketoisocaproate) generates signals triggering and acutely amplifying insulin secretion. As the pathway coupling metabolism with amplification is largely unknown, we aimed to narrow down the putative amplifying signals.
MATERIALS/METHODS: An experimental design was used which previously prevented glucose-induced, but not α-ketoisocaproate-induced insulin secretion. Isolated mouse islets were pretreated for one hour with medium devoid of fuels and containing the sulfonylurea glipizide in high concentration which closed all ATP-sensitive K(+) channels. This concentration was also applied during the subsequent examination of fuel-induced effects. In perifused or incubated islets, insulin secretion and metabolic parameters were measured.
The pretreatment decreased the islet ATP/ADP ratio. Whereas glucose and α-ketoisovalerate were ineffective or weakly effective, respectively, when tested separately, their combination strongly enhanced the insulin secretion. Compared with glucose, the strong amplifier α-ketoisocaproate caused less increase in NAD(P)H-fluorescence and less mitochondrial hyperpolarization. Compared with α-ketoisovalerate, α-ketoisocaproate caused greater increase in NAD(P)H-fluorescence and greater mitochondrial hyperpolarization. Neither α-ketoacid anion enhanced the islet ATP/ADP ratio during onset of the insulin secretion. α-Ketoisocaproate induced a higher pyruvate content than glucose, slowly elevated the citrate content which was not changed by glucose and generated a much higher acetoacetate content than other fuels. α-Ketoisovalerate alone or in combination with glucose did not increase the citrate content.
In β-cells, mitochondrial energy generation does not mediate acute metabolic amplification, but mitochondrial production of acetyl-CoA and supplemental acetoacetate supplies cytosolic metabolites which induce the generation of specific amplifying signals.
葡萄糖和其他一些燃料（例如α-酮异己酸）的β细胞代谢会产生触发和急性放大胰岛素分泌的信号。由于代谢与放大的途径在很大程度上是未知的，我们旨在缩小潜在的放大信号。
材料/方法：使用了一种实验设计，该设计先前阻止了葡萄糖诱导但不阻止α-酮异己酸诱导的胰岛素分泌。将分离的小鼠胰岛用不含燃料且含有高浓度磺酰脲类药物格列吡嗪的培养基预处理一小时，该浓度也应用于随后的燃料诱导作用的检查。在灌注或孵育的胰岛中，测量胰岛素分泌和代谢参数。
预处理降低了胰岛的 ATP/ADP 比值。虽然葡萄糖和α-酮异戊酸分别单独测试时无效或作用较弱，但它们的组合强烈增强了胰岛素分泌。与葡萄糖相比，强放大器α-酮异己酸引起的 NAD(P)H 荧光增加较少，线粒体超极化较少。与α-酮异戊酸相比，α-酮异己酸引起的 NAD(P)H 荧光增加更大，线粒体超极化更大。在胰岛素分泌开始时，α-酮酸阴离子都没有增强胰岛的 ATP/ADP 比值。α-酮异己酸诱导的丙酮酸含量高于葡萄糖，缓慢增加的柠檬酸含量不受葡萄糖影响，生成的乙酰乙酸含量远高于其他燃料。单独的α-酮异己酸或与葡萄糖一起使用都不会增加柠檬酸含量。
在β细胞中，线粒体能量生成不介导急性代谢放大，但线粒体生成的乙酰辅酶 A 和补充的乙酰乙酸提供细胞溶质代谢物，诱导产生特定的放大信号。
