Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
Biochem J. 2011 Apr 15;435(2):421-30. doi: 10.1042/BJ20101708.
In pancreatic β-cells, glucose-induced mitochondrial ATP production plays an important role in insulin secretion. The mitochondrial phosphate carrier PiC is a member of the SLC25 (solute carrier family 25) family and transports Pi from the cytosol into the mitochondrial matrix. Since intramitochondrial Pi is an essential substrate for mitochondrial ATP production by complex V (ATP synthase) and affects the activity of the respiratory chain, Pi transport via PiC may be a rate-limiting step for ATP production. We evaluated the role of PiC in metabolism-secretion coupling in pancreatic β-cells using INS-1 cells manipulated to reduce PiC expression by siRNA (small interfering RNA). Consequent reduction of the PiC protein level decreased glucose (10 mM)-stimulated insulin secretion, the ATP:ADP ratio in the presence of 10 mM glucose and elevation of intracellular calcium concentration in response to 10 mM glucose without affecting the mitochondrial membrane potential (Δψm) in INS-1 cells. In experiments using the mitochondrial fraction of INS-1 cells in the presence of 1 mM succinate, PiC down-regulation decreased ATP production at various Pi concentrations ranging from 0.001 to 10 mM, but did not affect Δψm at 3 mM Pi. In conclusion, the Pi supply to mitochondria via PiC plays a critical role in ATP production and metabolism-secretion coupling in INS-1 cells.
在胰腺β细胞中，葡萄糖诱导的线粒体 ATP 产生在胰岛素分泌中起着重要作用。线粒体磷酸盐载体 PiC 是 SLC25（溶质载体家族 25）家族的成员，它将 Pi 从细胞质转运到线粒体基质中。由于线粒体内的 Pi 是复合物 V（ATP 合酶）产生线粒体 ATP 的必需底物，并且影响呼吸链的活性，因此通过 PiC 的 Pi 转运可能是 ATP 产生的限速步骤。我们使用 INS-1 细胞通过 siRNA（小干扰 RNA）操纵来降低 PiC 表达，评估了 PiC 在胰腺β细胞代谢-分泌偶联中的作用。PiC 蛋白水平的相应降低降低了葡萄糖（10mM）刺激的胰岛素分泌、存在 10mM 葡萄糖时的 ATP:ADP 比值以及对 10mM 葡萄糖的细胞内钙离子浓度升高，而不影响 INS-1 细胞中的线粒体膜电位（Δψm）。在使用 1mM 琥珀酸盐的 INS-1 细胞线粒体部分的实验中，PiC 的下调降低了各种 Pi 浓度（从 0.001 到 10mM）下的 ATP 产生，但在 3mM Pi 下不影响 Δψm。总之，PiC 通过 PiC 将 Pi 供应给线粒体在 INS-1 细胞的 ATP 产生和代谢-分泌偶联中起着关键作用。
