Yau W M, Makhlouf G M
Am J Physiol. 1975 Jan;228(1):191-5. doi: 10.1152/ajplegacy.1975.228.1.191.
The mechanisms of water and ion transport in ascending and descending rat colon were compared using an everted open mucosal sac preparation. Net water flux, measured gravimetrically, was similar in both segments (15.3 plus or minus 1.2 and 13.7 plus or minus 1.3mul h(-1) mg(-1), NS). Net catonic flux J(Na+K),net anionic flux J(Cl-HCO3), and net solute flux Josm were also similar; but the constituents of these flux , namely JNA, JK, and JHCO3, were significantly different. The descending colon absorbed significantly less Na and secreted significantly more HCO3. Only the descending colon absorbed K, whereas net JK across the ascending colon was zero. The PD across either segment ranged from 3 to 7 mV, mucosal side negative. Consideration of net flux and electrochemical gradient indicated that in both segments Na was absorbed actively. The nature of Cl transport could not be ascertained. Assuming transmural movement, HCO3 was secreted (or H ion absorbed) actively. Only the descending colon absorbed K actively. Across the ascending colon K was distributed close to electrochemical equilibrium. The compostion of the absorbates was calculated from Ji/Jv after correction of Jv for filtered water. Both absorbates were equally hypertonic (448.5 plus orminus 9.3 and 421.7 plus or minus 13.2; NS.)The ascending colon absorbate contained a significantly higher Na concentration and no K. The descending colon absorbate contained 15 mM K, about 3 times the K concentration in the bathing solution. It was concluded that the ascending colon and descending colon displayed quantitative differences in Na absorption and HCO3 secretion and a qualitative difference in K transport.
采用外翻开放黏膜囊制备法比较了大鼠升结肠和降结肠水和离子转运的机制。通过重量法测量的净水流在两个肠段相似（分别为15.3±1.2和13.7±1.3μl·h⁻¹·mg⁻¹，无显著性差异）。净阳离子通量J(Na⁺+K)、净阴离子通量J(Cl⁻-HCO₃)和净溶质通量Josm也相似；但这些通量的组成成分，即JNa、JK和JHCO₃，有显著差异。降结肠吸收的Na明显较少，分泌的HCO₃明显较多。只有降结肠吸收K，而升结肠的净JK为零。任一肠段的跨膜电位范围为3至7mV，黏膜侧为负。对净通量和电化学梯度的考虑表明，两个肠段的Na均为主动吸收。无法确定Cl的转运性质。假设其跨膜移动，HCO₃是主动分泌的（或H⁺被吸收）。只有降结肠主动吸收K。在升结肠中，K的分布接近电化学平衡。吸收液的成分通过校正Jv中的滤过水后，根据Ji/Jv计算得出。两种吸收液的渗透压均为高渗（分别为448.5±9.3和421.7±13.2；无显著性差异）。升结肠吸收液中的Na浓度显著较高且不含K。降结肠吸收液中含有15mM K，约为浴液中K浓度的3倍。结论是升结肠和降结肠在Na吸收和HCO₃分泌方面存在量的差异，在K转运方面存在质的差异。
