Lappova Y L, Leibush B N
Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Science, St. Petersburg, Russia.
Gen Comp Endocrinol. 1995 Oct;100(1):1-9. doi: 10.1006/gcen.1995.1125.
The binding of 125I-insulin to cellular insulin receptors and the internalization of insulin-receptor complexes have been studied in isolated hepatocytes of frog and lamprey. Two classes of binding sites (Kd 10(-9) and 10(-8) M) were found in cells of both species. The molecular weight of the insulin receptor alpha-subunit was 130 kDa in both species. Internalization of bound 125I-insulin in both species was found in the temperature range 0 to 20 degrees. Cells "loaded" with 125I-insulin were used to estimate the fate of the internalized ligand. Release of internalized ligand from frog cells increased at temperatures ranging from 0 to 20 degrees. At 0 degrees the degraded 125I-insulin was 5%, at 5 degrees 7%, and at 20 degrees 17% of total radioactivity accumulated in the medium. In lamprey hepatocytes there was neither radioactivity accumulation in the incubation medium nor release from cells at all temperatures studied. The intracellular degradation of internalized 125I-insulin in frog hepatocytes was much lower than that in lamprey cells. In frog hepatocytes the specific binding of 125I-insulin was increased twofold in the presence of the lysosomal inhibitor chloroquine. In contrast no increase was found in lamprey hepatocytes. In conclusion, the processing pathways of internalized insulin in the cells of ectothermal and endothermal vertebrates are generally similar but in ectothermal animals all events take place at lower temperatures and at lower rates. The peculiarities of insulin processing in lamprey hepatocytes most likely result from the transformation of hepatocytes during the nonfeeding prespawning period.
在青蛙和七鳃鳗的离体肝细胞中，研究了¹²⁵I标记胰岛素与细胞胰岛素受体的结合以及胰岛素 - 受体复合物的内化过程。在这两种动物的细胞中均发现了两类结合位点（解离常数Kd分别为10⁻⁹和10⁻⁸ M）。两种动物胰岛素受体α亚基的分子量均为130 kDa。在0至20摄氏度的温度范围内，发现这两种动物细胞中¹²⁵I标记胰岛素的内化现象。用¹²⁵I标记胰岛素“负载”的细胞来评估内化配体的去向。青蛙细胞中内化配体的释放量在0至20摄氏度范围内增加。在0摄氏度时，培养基中累积的¹²⁵I标记胰岛素降解产物占总放射性的5%，5摄氏度时为7%，20摄氏度时为17%。在七鳃鳗肝细胞中，在所研究的所有温度下，孵育培养基中均无放射性累积，细胞也无释放现象。青蛙肝细胞中内化的¹²⁵I标记胰岛素的细胞内降解远低于七鳃鳗细胞。在青蛙肝细胞中，溶酶体抑制剂氯喹存在时，¹²⁵I标记胰岛素的特异性结合增加了两倍。相比之下，七鳃鳗肝细胞中未发现增加。总之，变温动物和恒温动物细胞中内化胰岛素的处理途径总体相似，但在变温动物中，所有事件都在较低温度下以较低速率发生。七鳃鳗肝细胞中胰岛素处理的特殊性很可能是由于非摄食产卵前期肝细胞的转变所致。
