Physiological and molecular biological studies on the pathogenesis of impaired insulin secretion in diabetes mellitus.

作为非胰岛素依赖型糖尿病（NIDDM）病理生理方面的主要特征之一，葡萄糖诱导的胰岛素分泌选择性损伤已为人们所熟知。另一方面，胰岛素分泌能力在对葡萄糖以外的刺激作出反应时反而增强。因此，我们直接使用膜片钳技术研究了电压依赖性Ca^<2+>通道（VDCC）的活性，该通道在细胞内Ca^<2+>水平的调节中起着非常重要的作用。利用遗传NIDDM GK大鼠胰岛分散获得的单个β细胞，全细胞记录Ca^<2+>通道电流的l型和t型。此外，为了探讨在不介导K_<ATP>通道关闭的情况下，通过糖代谢调节VDCC活性的细胞内机制，我们还利用制霉菌素法穿孔贴片。与对照组相比，GK β细胞中l型和t型VDCC活性在成员去极化后均显著增强。在对照β细胞中，在穿孔斑块中加载葡萄糖后，VDCC活性增强。然而，在GK β细胞中没有发现这种增强。这些现象似乎与GK大鼠NIDDM β细胞中胰岛素分泌能力受损的葡萄糖选择性密切相关。

As one of the major characteristics in pathophysiological aspects in noninsulin-dependent diabetes mellitus (NIDDM), the selective impairment of glucose-induced insulin secretion has been well known. On the other hand, the insulin secretory capacity is rather enhanced in response to the stimuli other than glucose. We, therefore, investigated the activity of voltage-dependent Ca^<2+> channel (VDCC) directly using the patch-clamp technique, which has a very important role on the regulation of intracellular Ca^<2+> levels. Using single beta-cells obtained by the dispersion of pancreatic islets of GK rats with genetically NIDDM,the L-and T-types of Ca^<2+> channel currents were recorded by whole cell recording. In addition, in order to investigate the intracellular mechanisms for modulating VDCC activities throuph glucose metabolism without mediating the K_<ATP> channel closure, the perforated patch using nystatin method was also utilized. Both of L-and T-type VDCC activities were found to be significautly enhanced after the membr anedepolarization in GK beta-cells when compared to the controls. In control beta-cells, the VDCC activities were more augmented after glucose loading in perforated patches. However, such an augmentation was not to be found in GK beta-cells. These phenomena seem to be closely related to the glucose selectivity of the impairment of insulin secretory capacity found in NIDDM beta cells of GK rats.