Teillet L, Tacnet F, Ripoche P, Corman B
Hôpital Sainte Périne, Paris, France.
Mech Ageing Dev. 1995 Apr 14;79(2-3):151-67. doi: 10.1016/0047-6374(94)01556-2.
The effects of aging on intestinal absorption of zinc and L-histidine were investigated in adult (10-month-old) and senescent (30-month-old) Wistar rats' brush-border membrane vesicles isolated from jejunum and ileum. Kinetic parameters of the zinc transport by the jejunal brush-border membrane were Jmax = 126 +/- 24 nmol.min-1.mg-1 protein and Km = 490 +/- 126 microM (10-month-old rats, n = 7). The transport of zinc was the same in the jejunum and the ileum of adult animals. In senescent rats, the zinc uptake was significantly lower in the distal part of the intestine than in the proximal one. A comparison of zinc uptake in 10- and 30-month-old rats showed that the transport capacity of the jejunum did not change with age but the ileal transport capacity decreased by 50%. This reduced uptake was associated with an increased cholesterol content of the brush-border membrane. The major site of L-histidine absorption was the jejunum, in both the 10- and 30-month-old animals. L-Histidine was co-transported with Na+. The kinetic parameters of the L-histidine carrier in the presence of Na+ were Jmax = 6.5 +/- 1.0 nmol.min-1.mg-1 protein and Km = 190 +/- 29 microM in the jejunum of 10-month-old rats (n = 12). Increasing the extra-vesicular concentration of zinc (0 --> 1 mM) reduced the uptake of L-histidine, and conversely increasing the concentration of L-histidine (0 --> 1 mM) reduced that of zinc: there was no evidence of transport of a complexed form [zinc-L-histidine] in brush-border membranes of the small intestine. During aging, the transport capacity of L-histidine by the jejunum decreased, whereas the ileal transport capacity was conserved. The modifications of absorptive capacity for zinc and L-histidine at the membrane level (loss of ileal function for zinc, and loss of jejunal function for amino acid) indicate that the normal aging of intestinal epithelial cells cannot be regarded as a decline in the overall transport of nutriments but as a combination of highly specific modifications of the various transport systems.
研究了衰老对成年（10月龄）和老年（30月龄）Wistar大鼠空肠和回肠分离的刷状缘膜囊泡中锌和L-组氨酸肠道吸收的影响。空肠刷状缘膜锌转运的动力学参数为Jmax = 126±24 nmol·min⁻¹·mg⁻¹蛋白质，Km = 490±126 μM（10月龄大鼠，n = 7）。成年动物空肠和回肠中的锌转运情况相同。在老年大鼠中，肠道远端的锌摄取显著低于近端。对10月龄和30月龄大鼠锌摄取的比较表明，空肠的转运能力不随年龄变化，但回肠的转运能力下降了50%。这种摄取减少与刷状缘膜胆固醇含量增加有关。在10月龄和30月龄动物中，L-组氨酸的主要吸收部位都是空肠。L-组氨酸与Na⁺协同转运。在10月龄大鼠空肠中，存在Na⁺时L-组氨酸载体的动力学参数为Jmax = 6.5±1.0 nmol·min⁻¹·mg⁻¹蛋白质，Km = 190±29 μM（n = 12）。增加细胞外锌浓度（0→1 mM）会降低L-组氨酸的摄取，反之，增加L-组氨酸浓度（0→1 mM）会降低锌的摄取：在小肠刷状缘膜中没有证据表明存在复合形式[锌-L-组氨酸]的转运。在衰老过程中，空肠对L-组氨酸的转运能力下降，而回肠的转运能力保持不变。锌和L-组氨酸在膜水平吸收能力的改变（回肠对锌功能丧失，空肠对氨基酸功能丧失）表明，肠道上皮细胞的正常衰老不能被视为营养物质整体转运的下降，而应看作是各种转运系统高度特异性改变的组合。
