L-glucose absorption in house sparrows (Passer domesticus) is nonmediated
L-glucose absorption in house sparrows (Passer domesticus) is nonmediated
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DOI：
10.1007/s00360-003-0403-3
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发表时间：
2004-03-01
影响因子：
2
通讯作者：
Karasov, WH
中科院分区：
文献类型：
--
作者：
Chang, MH;Chediack, JG;Karasov, WH
我们以前证明了在完整的家雀体内大量吸收L-葡萄糖，D-葡萄糖的立体异构体，被认为不与肠道的D-葡萄糖转运蛋白相互作用。一些研究结果对其他物种的这一假设提出了挑战。因此，我们在体外和体内对其进行了测试，基于以下原理：如果化合物（L-葡萄糖）的吸收是介导的，则其示踪剂的吸收将被高浓度的化合物本身或其他化合物（例如，D-葡萄糖），其吸收由相同的机制介导。另一种假设认为，L-葡萄糖吸收主要是细胞旁的，预测其在体内的吸收将增加（而不是减少）在D-葡萄糖的存在下，因为这一途径的渗透性被认为是增强时，Na+耦合的葡萄糖吸收发生。首先，使用完整的组织在体外，我们发现，示踪剂放射性标记的L-葡萄糖的摄取没有显着抑制高浓度（100 mM）的L-葡萄糖或3-O-甲基-D-葡萄糖，非代谢，但积极运输的D-葡萄糖类似物。其次，使用完整的家雀，我们发现，分数吸收的L-葡萄糖示踪剂显着增加，而不是减少，当灌胃沿着200 mM的3-O-甲基-D-葡萄糖。这一结果在另一个实验中得到证实，其中在肠道中存在食物的情况下与不存在食物的情况下相比，L-葡萄糖吸收分数显著更高。更大的吸收显然不是简单地由于更长的保留时间，因为没有发现保留时间之间的显着差异。我们的研究结果是一致的想法，L-葡萄糖是在一个非介导的方式，主要是通过细胞旁途径在体内吸收。
We previously demonstrated in intact house sparrows substantial absorption in vivo of L-glucose, the stereoisomer of D-glucose that is assumed not to interact with the intestine's D-glucose transporter. Results of some studies challenge this assumption for other species. Therefore, we tested it in vitro and in vivo, based on the principle that if absorption of a compound (L-glucose) is mediated, then absorption of its tracer will be competitively inhibited by high concentrations of either the compound itself or other compounds (e.g., D-glucose) whose absorption is mediated by the same mechanism. An alternative hypothesis that L-glucose absorption is primarily paracellular predicts that its absorption in vivo will be increased (not decreased) in the presence of D-glucose, because the permeability of this pathway is supposedly enhanced when Na+-coupled glucose absorption occurs. First, using intact tissue in vitro, we found that uptake of tracer-radiolabeled L-glucose was not significantly inhibited by high concentrations (100 mM) of either L-glucose or 3-O-methyl-D-glucose, a non-metabolizable but actively transported D-glucose analogue. Second, using intact house sparrows, we found that fractional absorption of the L-glucose tracer was significantly increased, not reduced, when gavaged along with 200 mM 3-O-methyl-D-glucose. This result was confirmed in another experiment where L-glucose fractional absorption was significantly higher in the presence vs. absence of food in the gut. The greater absorption was apparently not due simply to longer retention time of digesta, because no significant difference was found among retention times. Our results are consistent with the idea that L-glucose is absorbed in a non-mediated fashion, largely via the paracellular pathway in vivo.