Department of Physiology, Saga University Faculty of Medicine, 5-1-1 Nabeshima, Saga, 849-8501, Japan.
J Physiol Sci. 2009 Mar;59(2):87-96. doi: 10.1007/s12576-008-0012-8. Epub 2008 Dec 26.
The currents through the volume-regulated outwardly rectifying anion channel (VRAC) were measured in single ventricular myocytes obtained from streptozotocin (STZ)-induced diabetic mice, using whole-cell voltage-clamp method. In myocytes from STZ-diabetic mice, the density of VRAC current induced by hypotonic perfusion was markedly reduced, compared with that in the cells form normal control mice. Video-image analysis showed that the regulatory volume decrease (RVD), which was seen in normal cells after osmotic swelling, was almost lost in myocytes from STZ-diabetic mice. Some mice were pretreated with 3-O-methylglucose before STZ injection, to prevent the STZ's beta cell toxicity. In the myocytes obtained from such mice, the magnitude of VRAC current and the degree of RVD seen during hypotonic challenge were almost normal. Incubation of the myocytes from STZ-diabetic mice with insulin reversed the attenuation of VRAC current. These findings suggested that the STZ-induced chronic insulin-deficiency was an important causal factor for the attenuation of VRAC current. Intracellular loading of the STZ-diabetic myocytes with phosphatidylinositol 3,4,5-trisphosphate (PIP3), but not phosphatidylinositol 4,5-bisphosphate (PIP2), also reversed the attenuation of VRAC current. Furthermore, treatment of the normal cells with wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, suppressed the development of VRAC current. We postulate that an impairment PI3K-PIP3 pathway, which may be insulin-dependent, is responsible for the attenuation of VRAC currents in STZ-diabetic myocytes.
采用全细胞膜片钳技术，在链脲佐菌素（STZ）诱导的糖尿病小鼠的心室肌细胞中测量了体积调节外向整流阴离子通道（VRAC）的电流。与来自正常对照小鼠的细胞相比，来自 STZ 糖尿病小鼠的细胞中由低渗灌注诱导的 VRAC 电流密度明显降低。视频图像分析表明，在正常细胞中，渗透肿胀后出现的调节性体积减小（RVD）几乎在 STZ 糖尿病小鼠的心肌细胞中丢失。一些小鼠在 STZ 注射前用 3-O-甲基葡萄糖预处理，以防止 STZ 对β细胞的毒性。在从这些小鼠获得的心肌细胞中，VRAC 电流的幅度和低渗刺激期间观察到的 RVD 程度几乎正常。胰岛素孵育可逆转 VRAC 电流的衰减。这些发现表明，STZ 诱导的慢性胰岛素缺乏是 VRAC 电流衰减的重要原因。用三磷酸肌醇 3,4,5-三磷酸（PIP3）而不是二磷酸肌醇 4,5-二磷酸（PIP2）对内质网的 STZ 糖尿病心肌细胞进行负载，也可逆转 VRAC 电流的衰减。此外，用磷脂酰肌醇 3-激酶（PI3K）抑制剂wortmannin 处理正常细胞可抑制 VRAC 电流的发展。我们假设 PI3K-PIP3 途径的损伤，可能是胰岛素依赖性的，是 STZ 糖尿病心肌细胞中 VRAC 电流衰减的原因。
