Cova Emanuela, Laforenza Umberto, Gastaldi Giulia, Sambuy Yula, Tritto Simona, Faelli Alide, Ventura Ulderico
Institute of Human Physiology, University of Pavia, Italy.
J Nutr. 2002 Jul;132(7):1995-2003. doi: 10.1093/jn/132.7.1995.
The functional characteristics of the intestinal absorption and secretion of guanidine as a model of a nutritionally and metabolically essential organic cation were examined in the Caco-2 human intestinal cell line. Both apical and basolateral transport of [14C]-guanidine were studied using Caco-2 cells grown on polycarbonate permeable membranes. The basolateral-to-apical flux of [14C]-guanidine (i.e., its secretion) was quantitatively higher than the apical-to-basolateral transport (i.e., its absorption). When Na+ was replaced by K+ or Li+, both apical and basolateral accumulation were significantly inhibited. Studies using the cell monolayers and apical membrane vesicles obtained from Caco-2 cells showed a potential-independent mechanism of guanidine apical uptake and efflux. Conversely, basolateral uptake and efflux were membrane potential dependent. Kinetic analysis revealed that both saturable and nonsaturable mechanisms accounted for the apical and basolateral accumulations. The [14C]-guanidine efflux from cells through the apical and basolateral membranes was significantly reduced at 4 degrees C, suggesting carrier-mediated mechanisms. Moreover, the apical efflux was stimulated by an inwardly directed H+ gradient. Influx and efflux of [14C]-guanidine were unaffected by the presence of tetraethylammonium, cimetidine or decynium-22 in the donor compartment. Only quinine significantly reduced [14C]-guanidine entrance through apical and basolateral membranes and its exit through the basolateral membrane. In conclusion, our results suggest that the influx and the efflux through the apical membrane is mediated by different transporters, whereas transport across the basolateral membrane is mediated by a member of the organic cation transporter family with high affinity for guanidine.
在Caco-2人肠道细胞系中，研究了作为营养和代谢必需有机阳离子模型的胍的肠道吸收和分泌的功能特性。使用生长在聚碳酸酯可渗透膜上的Caco-2细胞研究了[14C] - 胍的顶端和基底外侧转运。[14C] - 胍从基底外侧到顶端的通量（即其分泌）在数量上高于从顶端到基底外侧的转运（即其吸收）。当Na +被K +或Li +取代时，顶端和基底外侧的积累均受到显著抑制。使用从Caco-2细胞获得的细胞单层和顶端膜囊泡的研究表明，胍的顶端摄取和流出是一种不依赖于电位的机制。相反，基底外侧摄取和流出依赖于膜电位。动力学分析表明，饱和和不饱和机制都参与了顶端和基底外侧的积累。[14C] - 胍从细胞通过顶端和基底外侧膜的流出在4℃时显著减少，表明是载体介导的机制。此外，顶端流出受到向内的H +梯度的刺激。[14C] - 胍的流入和流出不受供体区室中四乙铵、西咪替丁或癸鎓-22的存在的影响。只有奎宁显著减少了[14C] - 胍通过顶端和基底外侧膜的进入以及通过基底外侧膜的流出。总之，我们的结果表明，通过顶端膜的流入和流出由不同的转运体介导，而跨基底外侧膜的转运由对胍具有高亲和力的有机阳离子转运体家族的成员介导。
