通过细胞旁和跨细胞途径在短路兔回肠中双向移动的钠离子

Bidirectional sodium ion movements via the paracellular and transcellular routes across short-circuited rabbit ileum.

作者信息

Simmons N L, Naftalin R J

出版信息

Biochim Biophys Acta. 1976 Oct 19;448(3):426-50. doi: 10.1016/0005-2736(76)90298-4.

DOI:10.1016/0005-2736(76)90298-4

PMID:974142

Abstract

It has been confirmed that the agent 2,3,6-triaminopyrimidine decreases Na+ conductance in the paracellular pathway of rabbit ileum. 2. Triaminopyrimidine has been used as a means of measuring transcellular bidirectional Na+ flux, and also, of assessing the contribution of the paracellular pathway to transepithlial Na+ flux. 3. Reduction of Ringer [Na+] to 25 mM or incubation with 0.1 mM ouabain reduces paracellular Na+ permeability. This effect may be due to lateral space collapse. Ringer galactose increases serosa to mucosa Na+ flux by a stimulating reflux through the tight junctions. A proportion of net Na+ flux in control tissues is due to asymmetry generated in the paracellular pathway. It is likely that this passive asymmetry results from an osmotic pressure gradient across the tight-junction. 4. Measurement of the tissue isotope specific activity ratio together with bidirectional transcellular Na+ fluxes allows calculation of the four unidirectional fluxes across the mucosal and serosal boundaries. Values obtained for Na+ entry (J12) and exit (J21) across the mucosal boundary are 7.97 alnd 7.13 mumol-cm(-2)-h(-1) respectively. Entry flux (J12) is a saturable function of Ringer [Na+]. The calculated Km is 295 mM and the V is 17.6 mumul-cm(-2)-h(-1). Na+ entry flux is insensitive to ouabain (0.1 mM). Ouabain results in elevation of exit (J21) flux of Na+ across the brush border. D-Galactose causes a saturable increase in Na+ flux (J12) across the mucosal boundary; the Km for this relationship is 1.2 mM and the V 2.17 mumol-cm(-2)-h(-1). The stoichiometry between sugar and Na+ entry is applixmately 1:1. In contrast to the effect of galactose on entry flux, no change in Na+ efflux across the mucosal boundary is observed when Ringer [galactose] is raised. This finding is dissonant with the prediction of the Na+ -gradient hypothesis. The calculated values of exit (J23) and entry (J32) Na+ fluxes across the serosal border are 16.74 and 15.90 mumol-cm(-2)-h(-1). 0.1 mM ouabain markedly reduces both these unidirectional fluxes. This result is consistent with a serosal location of the Na+-pump. Serosal Na+ exit flux J23 increases as a hyperbolic function of Ringer [galactose]. A small galactose-dependent decrease in entry (J32) is also observed. 0.1 mM ouabain abolishes these galactose-dependent changes. 5. The present findings together with those in the previous paper are discussed in relation to the convective-diffusion model for sugar transport.

摘要

已证实试剂2,3,6 - 三氨基嘧啶可降低兔回肠细胞旁途径中的Na⁺电导。2. 三氨基嘧啶已被用作测量跨细胞双向Na⁺通量的手段，也是评估细胞旁途径对跨上皮Na⁺通量贡献的手段。3. 将林格氏液[Na⁺]降至25 mM或与0.1 mM哇巴因孵育会降低细胞旁Na⁺通透性。这种效应可能是由于侧向间隙塌陷。林格氏半乳糖通过刺激经紧密连接的反流增加浆膜到黏膜的Na⁺通量。对照组织中一部分净Na⁺通量是由于细胞旁途径中产生的不对称性。这种被动不对称可能是由跨紧密连接的渗透压梯度导致的。4. 测量组织同位素比活性以及双向跨细胞Na⁺通量可计算跨黏膜和浆膜边界的四个单向通量。跨黏膜边界的Na⁺进入（J12）和流出（J21）值分别为7.97和7.13 μmol·cm⁻²·h⁻¹。进入通量（J12）是林格氏液[Na⁺]的饱和函数。计算得出的Km为295 mM，V为17.6 μmol·cm⁻²·h⁻¹。Na⁺进入通量对哇巴因（0.1 mM）不敏感。哇巴因导致Na⁺通过刷状缘的流出（J21）通量升高。D - 半乳糖使跨黏膜边界的Na⁺通量（J12）呈饱和增加；这种关系的Km为1.2 mM，V为2.17 μmol·cm⁻²·h⁻¹。糖与Na⁺进入之间的化学计量比约为1:1。与半乳糖对进入通量的影响相反，当林格氏液[半乳糖]升高时，未观察到跨黏膜边界的Na⁺流出有变化。这一发现与Na⁺梯度假说的预测不一致。计算得出的跨浆膜边界的Na⁺流出（J23）和进入（J32）通量值分别为16.74和15.90 μmol·cm⁻²·h⁻¹。0.1 mM哇巴因显著降低这两个单向通量。这一结果与Na⁺泵位于浆膜一致。浆膜Na⁺流出通量J23作为林格氏液[半乳糖]的双曲线函数增加。还观察到进入（J32）有小的半乳糖依赖性降低。0.1 mM哇巴因消除了这些半乳糖依赖性变化。5. 结合前一篇论文中的发现，就糖转运的对流 - 扩散模型对当前研究结果进行了讨论。