Hardwick L L, Jones M R, Buddington R K, Clemens R A, Lee D B
Division of Nephrology, Veterans Administration Medical Center, Sepulveda, California 91343.
Am J Physiol. 1990 Nov;259(5 Pt 1):G720-6. doi: 10.1152/ajpgi.1990.259.5.G720.
Transport characteristics of Ca and Mg were compared at three different levels of the absorptive process in male (120-170 g) Wistar rats. Balance studies in intact rats revealed that fractional Ca absorption decreased with increased Ca intake so that net Ca absorption remained constant. Fractional Mg absorption decreased modestly with increased Mg intake so that net Mg absorption increased proportionately with increased dietary Mg. Everted duodenal sacs demonstrated the presence of active Ca absorption with serosal-to-mucosal (S/M) ratio of 2.65 +/- 0.20 (n = 6), which was greater than unity (P less than 0.001). In contrast, the S/M for Mg did not exceed unity. Mucosal duodenal Ca uptake exhibited a large saturable (Michaelis constant of 4.80 +/- 0.34 mM, maximal velocity of 4.71 +/- 0.13 nmol.min-1.mg-1) and a small nonsaturable component (0.12 +/- 0.01 nmol.min-1.mg-1) in 5-wk-old rats (120 g). In 72-wk-old rats (600 g) the diffusional component of Ca uptake became predominant, and the slope increased significantly to 0.32 +/- 0.01 (P less than 0.05). Duodenal Mg uptake was completely concentration dependent and exhibited no age-related changes.
在雄性（120 - 170克）Wistar大鼠吸收过程的三个不同水平上比较了钙和镁的转运特性。对完整大鼠的平衡研究表明，随着钙摄入量增加，钙的分数吸收降低，因此净钙吸收保持恒定。随着镁摄入量增加，镁的分数吸收适度降低，因此净镁吸收随膳食镁增加而成比例增加。外翻十二指肠囊显示存在主动钙吸收，浆膜到黏膜（S/M）比率为2.65±0.20（n = 6），大于1（P小于0.001）。相比之下，镁的S/M不超过1。5周龄大鼠（120克）十二指肠黏膜对钙的摄取表现出一个大的可饱和成分（米氏常数为4.80±0.34 mM，最大速度为4.71±0.13 nmol·min⁻¹·mg⁻¹）和一个小的不饱和成分（0.12±0.01 nmol·min⁻¹·mg⁻¹）。在72周龄大鼠（600克）中，钙摄取的扩散成分占主导，斜率显著增加至0.32±0.01（P小于0.05）。十二指肠对镁的摄取完全依赖于浓度，且未表现出与年龄相关的变化。
