Navab F, Winter C G
Department of Medicine, University of Arkansas for Medical Sciences, Little Rock 72205.
Am J Physiol. 1988 Apr;254(4 Pt 1):G631-6. doi: 10.1152/ajpgi.1988.254.4.G630.
Whole-thickness everted jejunal rings were used to measure uptake of L-tyrosine (L-Tyr), L-phenylalanine (L-Phe), and L-tryptophan (L-Trp) in 6-, 12-, and 24-mo-old rats. The rate of uptake of all three amino acids (1 mM) was significantly reduced after 20 min of incubation in 24-mo-old compared with 6-mo-old rats. Results of influx (2 min) of 0.5-40.0 mM L-Phe and L-Trp suggested an increased affinity but decreased capacity for the transporter with age; these differences were significant for L-Trp (P less than 0.05). Respective values for apparent Kt and Vmax were the following: L-Phe 6-mo-old rats, 5.46 mM and 1.03 mumol.g-1.2 min-1; 24-mo-old rats, 2.54 mM and 0.51 mumol.g-1.2 min-1; L-Trp 6-mo-old rats, 5.09 mM and 0.38 mumol.g-1.2 min-1; 24-mo-old rats, 3.20 mM and 0.25 mumol.g-1.2 min-1. Values for 12-mo-old rats fell in between the other two age groups.
采用全层外翻空肠环来测量6月龄、12月龄和24月龄大鼠对L-酪氨酸（L-Tyr）、L-苯丙氨酸（L-Phe）和L-色氨酸（L-Trp）的摄取。与6月龄大鼠相比，24月龄大鼠在孵育20分钟后，所有三种氨基酸（1 mM）的摄取率均显著降低。0.5 - 40.0 mM L-Phe和L-Trp的流入量（2分钟）结果表明，随着年龄增长，转运体的亲和力增加但转运能力下降；这些差异在L-Trp中具有统计学意义（P小于0.05）。表观Kt和Vmax的各自值如下：L-Phe，6月龄大鼠为5.46 mM和1.03 μmol·g-1·2 min-1；24月龄大鼠为2.54 mM和0.51 μmol·g-1·2 min-1；L-Trp，6月龄大鼠为5.09 mM和0.38 μmol·g-1·2 min-1；24月龄大鼠为3.20 mM和0.25 μmol·g-1·2 min-1。12月龄大鼠的值介于其他两个年龄组之间。
