Karbach U, Feldmeier H
Medizinische Klinik, Klinikum Innenstadt, University of Munich, Germany.
Dig Dis Sci. 1993 Oct;38(10):1815-24. doi: 10.1007/BF01296104.
In the absence of electrochemical gradients, mucosa-to-serosa Ca transport across the rat cecum is about six times higher than the serosa-to-mucosa flux, resulting in a marked Ca absorption, which is considerably higher when compared with Ca absorption reported for other intestinal segments. The voltage-clamp experiments reveal that 45% of the total mucosa-to-serosa Ca transport measured across the short-circuited tissue is cellular whereas 55% is paracellular. The serosa-to-mucosa Ca flux, however, is purely paracellular. Dexamethasone or 1,25(OH)2D3 has no effect on the Ca transport across the cecum. Diphosphonate, known to inhibit 1,25(OH)2D3 synthesis, abolishes cellular mucosa-to-serosa Ca transport but this effect can be restored by simultaneous exogenous 1,25(OH)2D3 application. It is concluded that the cecum is the site with the highest calcium absorption in the rat intestine. The cellular mucosa-to-serosa Ca transport is dependent on 1,25(OH)2D3 but cannot be increased by exogenous 1,25(OH)2D3 application, suggesting that the Ca carrier in this segment already under normal nutritional conditions works at the maximal level. Ca absorption across the proximal colon therefore seems to be of physiological importance in the regulation of intestinal Ca homeostasis.
在没有电化学梯度的情况下，大鼠盲肠黏膜到浆膜的钙转运比浆膜到黏膜的通量高约六倍，导致显著的钙吸收，与其他肠段报道的钙吸收相比要高得多。电压钳实验表明，在短路组织中测量的黏膜到浆膜的总钙转运中，45%是通过细胞途径，而55%是通过细胞旁途径。然而，浆膜到黏膜的钙通量完全是通过细胞旁途径。地塞米松或1,25(OH)₂D₃对盲肠的钙转运没有影响。已知抑制1,25(OH)₂D₃合成的二膦酸盐可消除细胞黏膜到浆膜的钙转运，但这种作用可通过同时外源性应用1,25(OH)₂D₃来恢复。得出的结论是，盲肠是大鼠肠道中钙吸收最高的部位。细胞黏膜到浆膜的钙转运依赖于1,25(OH)₂D₃，但外源性应用1,25(OH)₂D₃并不能增加，这表明在正常营养条件下该段的钙载体已处于最大工作水平。因此，近端结肠的钙吸收在肠道钙稳态调节中似乎具有重要的生理意义。
