Fowler F C, Banks R K, Mailliard M E
Department of Medicine, University of Florida, Gainesville 32610-0214.
Hepatology. 1992 Nov;16(5):1187-94.
Liver regeneration occurs after removal of or damage to a portion of the liver; it leads to restoration of the original liver mass. The activities of three sodium-dependent amino acid transporters--system A, system N and system ASC--were determined during a 5-day period of liver regeneration in the rat. Seventy-percent hepatectomy or laparotomy was performed in pairs of rats; these rats' livers were removed at different time points after surgery. Transport activity was determined through measurement of the Na(+)-dependent uptake of tritiated amino acids by isolated hepatic plasma membrane vesicles. System A activity, as measured by the Na(+)-dependent uptake of 2-aminoisobutyric acid, is increased in the regenerating liver 2 to 24 hr after surgery compared with that of controls. Kinetic analysis of 2-(methylamino)isobutyric acid uptake showed a 100% increase in the maximum velocity of system A transport in the hepatectomized animals with no change in the Michaelis constant, suggesting an increase in the number of system A transport proteins in the plasma membrane of regenerating liver. During liver regeneration, no changes were noted in the transport activities of system N and system ASC as measured by the uptake of glutamine and cysteine, respectively, in the presence of 2-(methylamino)isobutyric acid. Our work suggests that system A performs a unique role in the secondary active transport of its substrate neutral amino acids to meet the metabolic demands of regenerating liver.
肝脏部分切除或受损后会发生肝再生，从而使肝脏恢复至原来的重量。在大鼠肝再生的5天时间里，对三种钠依赖性氨基酸转运系统——A系统、N系统和ASC系统的活性进行了测定。将大鼠两两配对，分别实施70%肝切除术或剖腹术；在术后不同时间点取这些大鼠的肝脏。通过测量分离的肝细胞膜囊泡对氚标记氨基酸的钠依赖性摄取来确定转运活性。以2-氨基异丁酸的钠依赖性摄取来衡量，A系统的活性在术后2至24小时的再生肝脏中比对照组有所增加。对2-（甲氨基）异丁酸摄取的动力学分析表明，肝切除动物中A系统转运的最大速度增加了100%，而米氏常数没有变化，这表明再生肝脏质膜中A系统转运蛋白的数量增加。在肝再生过程中，分别以谷氨酰胺和半胱氨酸的摄取来衡量，N系统和ASC系统的转运活性在存在2-（甲氨基）异丁酸的情况下未发现变化。我们的研究表明，A系统在其底物中性氨基酸的继发性主动转运中发挥独特作用，以满足再生肝脏的代谢需求。
