Beta-adrenergic activation of solute coupled water uptake by toad skin epithelium results in near-isosmotic transport

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• 作者：Robert Nielsen ; Erik Hviid Larsen
• 关键词：Solute coupled water transport ; Isosmotic transport ; Hyposmotic transport ; Uphill water transport ; High resistance epithelium ; Lateral intercellular space ; Isoproterenol ; Cutaneous water uptake ; Anuran Amphibia
• 刊名：Comparative Biochemistry and Physiology - Part A ; Molecular & Integrative Physiology
• 出版年：2007
• 期刊代码：23_10956433
• 类别：abs
• 出版时间：September 2007
• 卷：148
• 期：1
• 页码：64-71
• 文件大小：344 K

摘要

Transepithelial potential (V_T), conductance (G_T), and water flow (J_V) were measured simultaneously with good time resolution (min) in isolated toad (Bufo bufo) skin epithelium with Ringer on both sides. Inside application of 5 μM isoproterenol resulted in the fast increase in G_T from 1.2 ± 0.3 to 2.4 ± 0.4 mS·cm^{− 2} and slower increases in equivalent short circuit current, I_SC^Eqv = − G_T × V_T, from 12.7 ± 3.2 to 33.1 ± 6.8 μA cm^{− 2}, and J_V from 0.72 ± 0.17 to 3.01 ± 0.49 nL cm^{− 2} s^{− 1}. Amiloride in the outside solution abolished I_SC^Eqv ( − 1.6 ± 0.1 μA cm^{− 2}) while J_V decreased to 0.50 ± 0.15 nL cm^{− 2}·s^{− 1}, which is significantly different from zero. Isoproterenol decreased the osmotic concentration of the transported fluid, C_osm ≈ 2 × I_SC^Eqv/J_V, from 351 ± 72 to 227 ± 28 mOsm (Ringer's solution: 252.8 mOsm). J_V depicted a saturating function of [Na⁺]_out in agreement with Na⁺ self-inhibition of ENaC. Ouabain on the inside decreased I_SC^Eqv from 60 ± 10 to 6.1 ± 1.7 μA cm^{− 2}, and J_V from 3.34 ± 0.47 to 1.40 ± 0.24 nL cm^{− 2}·s^{- 1}. Short-circuited preparations exhibited a linear relationship between short-circuit current and J_V with a [Na⁺] of the transported fluid of 130 ± 24 mM ([Na⁺]_{Ringer's solution} = 117.4 mM). Addition of bumetanide to the inside solution reduced J_V. Water was transported uphill and J_V reversed at an excess outside osmotic concentration, ΔC_S,rev = 28.9 ± 3.9 mOsm, amiloride decreased ΔC_S,rev to 7.5 ± 1.5 mOsm. It is concluded that water uptake is accomplished by osmotic coupling in the lateral intercellular space (lis), and hypothesized that a small fraction of the Na⁺ flux pumped into lis is recirculated via basolateral NKCC transporters.