Zhang C, Husted R F, Stokes J B
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, USA.
Am J Physiol. 1996 Jan;270(1 Pt 2):F131-40. doi: 10.1152/ajprenal.1996.270.1.F131.
The rat inner medullary collecting duct is capable of secreting anions. We previously showed that adenosine 3',5'-cyclic monophosphate (cAMP) stimulates anion secretion; the apical membrane anion exit pathway activated by cAMP appears to be the cystic fibrosis transmembrane conductance regulator Cl- channel. The present experiments were designed to test the hypothesis that the entry pathway across the basolateral membrane is a Cl-/HCO3- exchanger operating in parallel with an Na+/H+ exchanger. We investigated the mechanism by measuring cell Cl-, cell pH, and short-circuit current under a variety of conditions designed to uncover these pathways. cAMP agonists caused little change in cell Cl-, but they produced a consistent intracellular acidification. This acidification was dependent on HCO3-, but not on Cl-, and was not inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). The presence of the basolateral Cl-/HCO3- exchanger was demonstrated by several maneuvers, and its activity was inhibited by DIDS. Applied to the basolateral solution, DIDS did not inhibit the cAMP-dependent anion current but actually stimulated it. We conclude that cAMP-stimulated anion secretion does not require activation of the basolateral Cl-/HCO3- exchanger. The transporter responsible for Cl- entry across the basolateral membrane remains unknown and is not inhibited by a variety of anion transport inhibitors, including DIDS, bumetanide, and hydrochlorothiazide. The cell acidification induced by cAMP appears to be independent of acid secretion and is the result of activation of one or more HCO3- exit pathways that are resistant to DIDS but are inhibited by a nonspecific anion transport inhibitor, 5-nitro-2-(3-phenylpro-pylamino) benzoic acid. We present a revised model for anion transport by the rat inner medullary collecting duct.
大鼠肾内髓集合管能够分泌阴离子。我们之前表明，3',5'-环磷酸腺苷（cAMP）可刺激阴离子分泌；cAMP激活的顶端膜阴离子排出途径似乎是囊性纤维化跨膜传导调节因子氯离子通道。本实验旨在检验以下假说：跨基底外侧膜的进入途径是一种与钠/氢交换体并行运作的氯/碳酸氢根交换体。我们通过在多种旨在揭示这些途径的条件下测量细胞内氯离子、细胞pH值和短路电流来研究其机制。cAMP激动剂对细胞内氯离子影响不大，但会导致细胞内持续酸化。这种酸化依赖于碳酸氢根，而非氯离子，且不受4,4'-二异硫氰基芪-2,2'-二磺酸（DIDS）抑制。通过多种操作证实了基底外侧氯/碳酸氢根交换体的存在，其活性受DIDS抑制。将DIDS应用于基底外侧溶液时，它并不抑制cAMP依赖性阴离子电流，反而会刺激该电流。我们得出结论，cAMP刺激的阴离子分泌不需要激活基底外侧氯/碳酸氢根交换体。负责氯离子跨基底外侧膜进入的转运体仍然未知，且不受包括DIDS、布美他尼和氢氯噻嗪在内的多种阴离子转运抑制剂的抑制。cAMP诱导的细胞酸化似乎与酸分泌无关，是一种或多种对DIDS有抗性但受非特异性阴离子转运抑制剂5-硝基-2-(3-苯基丙基氨基)苯甲酸抑制的碳酸氢根排出途径激活的结果。我们提出了大鼠肾内髓集合管阴离子转运的修订模型。
