Noma Y, Bonner-Weir S, Latimer J B, Davalli A M, Weir G C
Joslin Diabetes Center, Brigham and Women's Hospital, Boston, Massachusetts 02215, USA.
Endocrinology. 1996 Apr;137(4):1485-91. doi: 10.1210/endo.137.4.8625927.
Glucokinase (GK) plays a key role in the regulation of glucose-induced insulin secretion, and questions have been raised about its relationship to the glucose transporter GLUT2 and its function in diabetes. This study examined the location of immunostained GK and GLUT2 in beta-cells using confocal microscopy. On double stained sections from pancreases of normal fed rats, GLUT2 Texas Red staining was restricted to the plasma membrane, and GK fluorescein isothiocyanate staining was found in a limited area of cytoplasm that was perinuclear with slight extension toward the apical pole. The GK staining occupied 8.6 +/- 1.7% of total cytoplasmic area and was almost never adjacent to the GLUT2 staining of the plasma membrane. To determine whether the GK staining pattern is altered by metabolic perturbation, normal rats were made acutely hyperglycemic with iv glucose injections; after 20 min the GK staining changed from being localized to become diffusely distributed throughout the cytoplasm. To examine the influence of chronic hyperglycemia, rats were subjected to 90% partial pancreatectomy (Px), which produced glucose levels of 10.9-20.8 mM. When studied 6 or 14 days after Px, those rats with glucose levels greater than 17.7 mM had an altered GK staining pattern that was variable; in some beta-cells GK staining was diffuse and in others the localized staining pattern was preserved. GLUT2 staining was reduced overall, but variability between cells was observed, unlike the more uniform reductions seen with hyperglycemia of longer duration. Other rats received islet transplants to prevent hyperglycemia after Px; their GK and GLUT2 staining patterns were normal. These findings indicate that GK is translocated in association with acute and chronic hyperglycemia. The translocation of this key enzyme for glucose recognition by beta-cells may lead to altered rates of insulin secretion during acute perturbations of fuel provision and in the diabetic state.
葡萄糖激酶（GK）在葡萄糖诱导的胰岛素分泌调节中起关键作用，其与葡萄糖转运蛋白GLUT2的关系及其在糖尿病中的功能也引发了诸多问题。本研究利用共聚焦显微镜检查了β细胞中免疫染色的GK和GLUT2的定位。在正常喂养大鼠胰腺的双重染色切片上，GLUT2德克萨斯红染色局限于质膜，而GK异硫氰酸荧光素染色则见于核周有限的细胞质区域，并向顶端极稍有延伸。GK染色占细胞质总面积的8.6±1.7%，几乎从不与质膜的GLUT2染色相邻。为了确定GK染色模式是否因代谢紊乱而改变，通过静脉注射葡萄糖使正常大鼠急性高血糖；20分钟后，GK染色从局部化变为弥漫分布于整个细胞质。为了研究慢性高血糖的影响，对大鼠进行90%胰腺部分切除术（Px），其血糖水平为10.9 - 20.8 mM。在Px后6天或14天进行研究时，那些血糖水平高于17.7 mM的大鼠，其GK染色模式发生改变且具有变异性；在一些β细胞中，GK染色是弥漫性的，而在另一些细胞中，局部染色模式得以保留。GLUT2染色总体上减少，但细胞间存在变异性，这与持续时间较长的高血糖所见的更均匀减少不同。其他大鼠接受胰岛移植以防止Px后出现高血糖；它们的GK和GLUT2染色模式正常。这些发现表明，GK会随着急性和慢性高血糖而发生易位。这种β细胞识别葡萄糖的关键酶的易位可能导致在急性燃料供应扰动期间和糖尿病状态下胰岛素分泌速率发生改变。
