Mackenzie I L, Donaldson R M
J Clin Invest. 1972 Sep;51(9):2465-71. doi: 10.1172/JCI107060.
Calcium, but not other divalent cations, is required for optimal uptake of intrinsic factor-bound (57)Co-labeled cyanocobalamin (IFB(12)) by microvillous membranes isolated from hamster ileal-absorptive cells. Chelation of divalent cations by disodium ethylenediaminetetraacetate (EDTA) promptly removes IFB(12) previously attached to microvillous membranes. High concentrations of CaCl(2) or MgCl(2) also markedly inhibit membrane uptake of IFB(12) and rapidly remove previously attached IFB(12). Similarly, reduction of pH to below 5.4 prevents membrane attachment of IFB(12) and removes virtually all IFB(12) already bound to microvillous membranes. The effects of calcium depletion, increased salt concentrations, and acidification on membrane uptake of IFB(12) were completely reversible. These findings are consistent with the concept that the formation of calcium salt bridges is essential for attachment of IFB(12) to the ileal-absorptive surface.
从仓鼠回肠吸收细胞分离出的微绒毛膜，要实现对与内因子结合的（57）钴标记氰钴胺素（IFB12）的最佳摄取，需要钙而非其他二价阳离子。乙二胺四乙酸二钠（EDTA）对二价阳离子的螯合作用能迅速去除先前附着在微绒毛膜上的IFB12。高浓度的氯化钙或氯化镁也会显著抑制微绒毛膜对IFB12的摄取，并迅速去除先前附着的IFB12。同样，将pH值降低至5.4以下会阻止IFB12与膜的附着，并几乎去除所有已与微绒毛膜结合的IFB12。钙耗竭、盐浓度增加和酸化对微绒毛膜摄取IFB12的影响是完全可逆的。这些发现与钙盐桥的形成对于IFB12附着于回肠吸收表面至关重要这一概念相符。
