Koeppen B, Pappas C, Manger T, Oyler A
Division of Nephrology, University of Connecticut Health Center, Farmington.
Kidney Int Suppl. 1991 Jul;33:S131-5.
The OMCDi secretes Cl- when perfused and bathed with symmetrical solutions. The route for this transepithelial Cl- movement appears to be the paracellular pathway, and the driving force is the lumen positive voltage generated by the process of electrogenic H+ secretion. Currently, there is no evidence to support the existence of a significant transcellular route for transepithelial Cl- movement. Although the primary function of the OMCDi is related to urine acidification, Cl- plays an important role in this process. The basolateral membrane of the OMCDi cell contains a band-3 related Cl-/HCO3- antiporter and a Cl- conductance. The Cl-/HCO3- antiporter serves as the primary route for the efflux of HCO3- generated during the process of H+ secretion. The Cl- conductance allows Cl- brought into the cell by the antiporter to recycle across this membrane. This conductance also serves to maintain cell charge balance. Accordingly, for each equivalent of H+ leaving the cell across the apical membrane, a Cl- equivalent exits the cell across the basolateral membrane. Based on whole-cell patch-clamp studies, this Cl- conductance is blocked by the Cl- channel blocker DPC. This conductance may also have a finite permeability to HCO3-, and thus could serve as a secondary route for cellular HCO3- efflux. Lastly, the conductance is activated by the beta-adrenergic agonist isoproterenol.
当用对称溶液灌注和浸泡时，外髓集合管内段（OMCDi）会分泌氯离子。这种跨上皮氯离子移动的途径似乎是细胞旁途径，驱动力是由电生性氢离子分泌过程产生的管腔正电压。目前，没有证据支持存在一条重要的跨细胞途径用于跨上皮氯离子移动。尽管外髓集合管内段的主要功能与尿液酸化有关，但氯离子在这一过程中起着重要作用。外髓集合管内段细胞的基底外侧膜含有一种带3相关的氯/碳酸氢根反向转运体和一种氯电导。氯/碳酸氢根反向转运体是氢离子分泌过程中产生的碳酸氢根外流的主要途径。氯电导使由反向转运体带入细胞的氯离子能跨此膜再循环。这种电导也有助于维持细胞电荷平衡。因此，对于每一个通过顶端膜离开细胞的氢离子当量，一个氯离子当量会通过基底外侧膜离开细胞。基于全细胞膜片钳研究，这种氯电导被氯通道阻滞剂DPC阻断。这种电导对碳酸氢根可能也有一定的通透性，因此可作为细胞内碳酸氢根外流的第二条途径。最后，这种电导被β-肾上腺素能激动剂异丙肾上腺素激活。
