Ghishan F K, Parker P, Nichols S, Hoyumpa A
Pediatr Res. 1984 Mar;18(3):235-9. doi: 10.1203/00006450-198403000-00003.
Young animals absorb and retain more calcium (Ca) than their older counterparts. The mechanism(s) for this age-related difference and the kinetics of intestinal calcium transport during maturation are not known. We determined, therefore, the unidirectional uptake and the transmural flux of [45Ca] in everted duodenal and jejunal sacs of suckling, weanling, adolescent, and adult rats using [3H] dextran as a marker of adherent mucosal volume. These measurements were carried out over a wide range of Ca concentrations (0.5-30 mM). Results indicate an evolving pattern of intestinal calcium transport with different kinetic characteristics emerging as the animals matured. The active component of transport became more pronounced with increasing age. In adult rats Km and Jmax of [45Ca] duodenal and jejunal uptake were several-fold greater than corresponding values for suckling rats. Transport at higher calcium concentrations (10-30 mM) was non-saturable, and the permeability coefficient decreased with age. The transition to a more saturable process occurred around the time of weaning. These findings suggest that intestinal calcium transport is characterized by a maturation pattern that starts with a predominantly passive system during infancy and changes to a saturable active mechanism during maturation.
幼年动物比成年动物吸收和保留更多的钙（Ca）。这种与年龄相关差异的机制以及成熟过程中肠道钙转运的动力学尚不清楚。因此，我们以[3H]葡聚糖作为黏附黏膜体积的标志物，测定了乳鼠、断奶幼鼠、青春期大鼠和成年大鼠翻转十二指肠和空肠囊对[45Ca]的单向摄取和跨壁通量。这些测量是在广泛的钙浓度范围（0.5 - 30 mM）内进行的。结果表明，随着动物成熟，肠道钙转运呈现出一种不断演变的模式，具有不同的动力学特征。随着年龄增长，转运的活性成分变得更加明显。成年大鼠十二指肠和空肠对[45Ca]摄取的Km和Jmax比乳鼠的相应值大几倍。在较高钙浓度（10 - 30 mM）下的转运是不饱和的，并且渗透系数随年龄降低。向更具饱和性的过程的转变发生在断奶前后。这些发现表明，肠道钙转运的特征是一种成熟模式，在婴儿期以主要被动系统开始，在成熟过程中转变为可饱和的主动机制。
