Quigley Raymond, Baum Michel
Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, 75235-9063, USA.
Am J Physiol Renal Physiol. 2002 Sep;283(3):F525-31. doi: 10.1152/ajprenal.00005.2002.
The early proximal tubule preferentially reabsorbs organic solutes and bicarbonate over chloride ions, resulting in a luminal fluid with a higher chloride concentration than that in blood. From this late proximal tubular fluid, one-half of NaCl reabsorption by the adult proximal tubule is active and transcellular and one-half is passive and paracellular. The purpose of the present in vitro microperfusion study was to determine the characteristics of passive chloride transport and permeability properties of the adult and neonatal proximal straight tubules (PST). In tubules perfused with a late proximal tubular fluid, net passive chloride flux was 131.7 +/- 37.7 pmol x mm(-1) x min(-1) in adult tubules and -17.1 +/- 23.3 pmol x mm(-1) x min(-1) in neonatal proximal tubules (P < 0.01). Chloride permeability was 10.94 +/- 5.21 x 10(-5) cm/s in adult proximal tubules and -1.26 +/- 1.84 x 10(-5) cm/s in neonatal proximal tubules (P < 0.05). Thus neonatal PST have a chloride permeability not different from zero and have no net passive chloride transport. Bicarbonate permeability is also less in neonates than adults in this segment (-0.07 +/- 0.03 x 10(-5) vs. 0.93 +/- 0.27 x 10(-5) cm/s, P < 0.01). Neonatal PST have higher sodium-to chloride and bicarbonate-to-chloride permeability ratios than adult PST. However, mannitol and sucrose permeabilities were not different in adult proximal tubules and neonatal PST. Transepithelial resistance was measured using current injection and cable analysis. The resistance was 6.7 +/- 0.7 Omega x cm(2) in adult tubules and 11.3 +/- 1.4 Omega x cm(2) in neonatal PST (P < 0.01). In conclusion, there are significant maturational changes in the characteristics of the PST paracellular pathway affecting transport in this nephron segment.
早期近端小管优先重吸收有机溶质和碳酸氢根而非氯离子，导致管腔液中氯离子浓度高于血液中的氯离子浓度。在成人近端小管中，来自这种晚期近端小管液的氯化钠重吸收有一半是主动跨细胞的，另一半是被动细胞旁的。本体外微灌注研究的目的是确定成人和新生儿近端直小管（PST）被动氯离子转运的特征和通透性特性。在用晚期近端小管液灌注的小管中，成人小管的净被动氯离子通量为131.7±37.7 pmol·mm⁻¹·min⁻¹，新生儿近端小管为-17.1±23.3 pmol·mm⁻¹·min⁻¹（P<0.01）。成人近端小管的氯离子通透性为10.94±5.21×10⁻⁵ cm/s，新生儿近端小管为-1.26±1.84×10⁻⁵ cm/s（P<0.05）。因此，新生儿PST的氯离子通透性与零无异，且无净被动氯离子转运。在该节段中，新生儿的碳酸氢根通透性也低于成人（-0.07±0.03×10⁻⁵ vs. 0.93±0.27× l0⁻⁵ cm/s，P<0.01）。新生儿PST的钠氯和碳酸氢根氯通透性比值高于成人PST。然而，成人近端小管和新生儿PST的甘露醇和蔗糖通透性并无差异。使用电流注入和电缆分析测量跨上皮电阻。成人小管的电阻为6.7±0.7Ω·cm²，新生儿PST为11.3±1.4Ω·cm²（P<0.01）。总之，PST细胞旁途径的特性存在显著的成熟变化，影响该肾单位节段的转运。
