Wilson P W, Lawson D E
Pflugers Arch. 1980 Dec;389(1):69-74. doi: 10.1007/BF00587930.
Uptake of Ca2+ by vesicle preparation of chick intestinal brush-border membranes was rapid and extensive. With tracer quantities of Ca2+ uptake was complete in 10 min whereas with 2.0 mM Ca2+ maximum uptake by the vesicles occurred after one hour incubation. The maximum concentration of Ca2+ found in the vesicles was four times greater than the external Ca2+ concentration showing that the majority of the Ca2+ was membrane bound. The Ca2+ taken up by the vesicles was probably bound to the vesicle's interior since it was not replaced by exposure of loaded vesicles to La3+ (5 mM). The uptake of Ca2+ by the vesicles at different Ca2+ concentrations was analyzed and a high affinity Ca2+ binding site was found with an association constant for Ca2+ of 5 x 10(-5) M. More of the sites were found in the duodenum than the ileum and vitamin D increases the number of these sites.
鸡小肠刷状缘膜囊泡制剂对Ca2+的摄取迅速且广泛。对于微量Ca2+，摄取在10分钟内完成，而对于2.0 mM Ca2+，囊泡在孵育1小时后出现最大摄取量。囊泡中发现的Ca2+最大浓度比外部Ca2+浓度大四倍，表明大部分Ca2+与膜结合。囊泡摄取的Ca2+可能与囊泡内部结合，因为加载的囊泡暴露于La3+（5 mM）时，Ca2+并未被取代。分析了不同Ca2+浓度下囊泡对Ca2+的摄取，发现了一个高亲和力的Ca2+结合位点，Ca2+的缔合常数为5×10(-5) M。十二指肠中发现的这些位点比回肠中更多，维生素D会增加这些位点的数量。
