FIGURE 2.

Intercalated cell marker labeling in mouse cortical collecting duct (CCD) and connecting tubule (CNT). Characteristic immunolabeling of the three distinct intercalated cell subtypes in the CNT (top panels) and CCD (bottom panels) are shown by differential interference contrast microscopy (DIC). Type A intercalated cells express the basolateral anion exchanger AE1, apical H⁺-ATPase, and the basolateral ammonia transporter Rhbg. Type B intercalated cells express the apical anion exchanger, pendrin, and basolateral H⁺-ATPase, but not AE1 or Rhbg. Non-A, non-B intercalated cells express apical pendrin, apical H⁺-ATPase, and basolateral Rhbg, but not AE1. Left column: double labeling for pendrin (blue) and AE1 (brown), the latter of which is definitive for type A intercalated cells; apical pendrin (blue) is present in type B and non-A, non-B intercalated cells. Pendrin labeling is exclusively in AE1-negative cells. Middle column: double labeling for AE1 (brown) and the a4 subunit of H⁺-ATPase (blue). Type A intercalated cells (AE1-positive) have apical H⁺-ATPase label. Type B intercalated cells have basolateral H⁺-ATPase label (arrows), as well as diffuse apical label, which correlates with cytoplasmic vesicle labeling shown by immunogold electron microscopy. Type B intercalated cells are uncommon in the CNT, but represent virtually all of the non-A intercalated cells in the CCD. In the CNT, the majority of non-A intercalated cells have apical H⁺-ATPase label, but no basolateral label. These are non-A, non-B intercalated cells. Right column: double labeling for pendrin (blue) and Rhbg (brown). Type B intercalated cells and non-A, non-B intercalated cells, both pendrin-positive, can be discriminated by basolateral Rhbg expression. Non-A, non-B intercalated cells, which express basolateral Rhbg (arrowheads), are the predominant pendrin-positive cell type in the CNT. Type B intercalated cells do not express detectable Rhbg (arrows) and comprise virtually all of the pendrin-positive cells in the CCD. Rhbg immunolabel is also present in type A intercalated cells (open arrows), CNT cells, and CCD principal cells. [From Verlander and Clapp (216), with permission from Elsevier.]