Intercalated cell subtypes in connecting tubule and cortical collecting duct of rat and mouse

At least two populations of intercalated cells, type A and type B, exist in the connecting tubule (CNT), initial collecting tubule (ICT), and cortical collecting duct (CCD). Type A intercalated cells secrete protons via an ap ical H+- ATPase and reabsorb bicarbonate by a band 3-like Cl-/HCO3- exchang er, AE1, located in the basolateral plasma membrane. Type B intercalated ce lls secrete bicarbonate by an apical Cl-/HCO3- exchanger that is distinct f rom AE1 and remains to be identified. They express H+-ATPase in the basolat eral plasma membrane and in vesicles throughout the cytoplasm. A third type of intercalated cell with apical H+-ATPase, but no AE1, has been described in the CNT and CCD of both rat and mouse. The prevalence of the third cell type is not known. The aim of this study was to characterize and quantify intercalated cell subtypes, including the newly described third non A-non B cell, in the CNT, ICT, and CCD of the rat and mouse. A triple immunolabeli ng procedure was developed in which antibodies to H+-ATPase and band 3 prot ein were used to identify subpopulations of intercalated cells, and segment -specific antibodies were used to identify distal tubule and collecting duc t segments. In both rat and mouse, intercalated cells constituted approxima tely 40% of the cells in the CNT, ICT, and CCD. Type A, type B, and non A-n on B intercalated cells were observed in all of the three segments, with ty pe A cells being the most prevalent in both species. In the mouse, however, non A-non B cells constituted more than half of the intercalated cells in the CNT, 39% in the ICT, and 22% in the CCD, compared with 14, 7, and 5%, r espectively, in the rat. In contrast, type B intercalated cells accounted f or only 8 to 16% of the intercalated cells in the three segments in the mou se compared with 26 to 39% in the rat. It is concluded that striking differ ences exist in the prevalence and distribution of the different types of in tercalated cells in the CNT, ICT, and CCD of rat and mouse. In the rat, the non A-non B cells are fairly rare, whereas in the mouse, they constitute a major fraction of the intercalated cells, primarily at the expense of the type B intercalated cells.