Hu M S, Kayne L H, Willsey P A, Koteva A B, Jamgotchian N, Lee D B
Medical Service, Veterans Health Affairs Medical Center, Sepulveda 91343.
Am J Physiol. 1993 Feb;264(2 Pt 1):G319-24. doi: 10.1152/ajpgi.1993.264.2.G319.
Ileum displays little active transcellular calcium (Ca2+) absorption but is credited with the bulk of Ca2+ absorbed in vivo. We examined the effect of taurodeoxycholic acid (TDC, 2 mM), a bile salt, on mannitol (MN, a marker of intercellular solute traffic) and Ca2+ fluxes in rat ileum. In the absence of electrochemical gradients between the mucosal (M) and serosal (S) bathing media in an Ussing chamber, net flux (Jnet) was observed in the S-to-M direction for both MN and Ca2+, i.e., the unidirectional secretory S-to-M flux (Js-->m) exceeded the absorptive M-to-S flux (Jm-->s). Mucosal TDC caused simultaneous increase in transepithelial conductance and Js-->m for both MN and Ca2+. This was followed by even greater increases in MN and Ca2+ Jm-->s, so that ultimately Jm-->s equaled Js-->m in each case. In control tissue, Js-->m for Ca2+ appeared to permeate exclusively through the intercellular MN pathway while part of Jm-->s for Ca2+ appeared to traverse through a non-MN route. After the TDC-induced increase in intercellular solute permeability, both Ca2+ fluxes appeared to traverse through the aqueous MN conduit. During the postprandial state, the presence of bile salts and the relative abundance of Ca2+ in ileal lumen can cause bulk Ca2+ absorption through the intercellular pathway.
回肠几乎没有活跃的跨细胞钙（Ca2+）吸收，但在体内吸收的大部分Ca2+都归功于回肠。我们研究了牛磺去氧胆酸（TDC，2 mM），一种胆盐，对大鼠回肠中甘露醇（MN，细胞间溶质转运的标志物）和Ca2+通量的影响。在Ussing chamber中黏膜（M）和浆膜（S）浴液介质之间不存在电化学梯度的情况下，观察到MN和Ca2+的净通量（Jnet）均从S向M方向，即单向分泌性S到M通量（Js-->m）超过吸收性M到S通量（Jm-->s）。黏膜TDC导致MN和Ca2+的跨上皮电导和Js-->m同时增加。随后MN和Ca2+的Jm-->s进一步大幅增加，以至于最终在每种情况下Jm-->s都等于Js-->m。在对照组织中，Ca2+的Js-->m似乎仅通过细胞间MN途径渗透，而Ca2+的部分Jm-->s似乎通过非MN途径穿过。在TDC诱导细胞间溶质通透性增加后，两种Ca2+通量似乎都通过水性MN通道穿过。在餐后状态下，胆盐的存在以及回肠腔中Ca2+的相对丰度可导致通过细胞间途径的大量Ca2+吸收。
