Distribution of Cl-/HCO3- exchange and intercalated cells in rabbit cortical collecting duct

At least two cortical collecting duct (CCD) intercalated cell populations mediate HCO3- secretion and reabsorption. The present study examined the membrane location of intercalated cell Cl-/base exchange activity and the axial distribution of CCD intercalated cells. CCD were studied using in vitro microperfusion in CO2/HCO3(-)-containing solutions; intracellular pH was measured using 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The A-type intercalated cell (A cell) and B-type intercalated cell (B cell) were identified functionally by the absence and presence of apical Cl-/HCO3- exchange activity, respectively. When a 0 mM Cl-, 0 mM HCO3- luminal solution was used, removal of Cl- from the peritubular solution caused intracellular alkalinization in all B cells. The alkalinization required neither extracellular Na+ nor changes in membrane potential. Peritubular 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) (10(-4) M) inhibited A cell but not B cell basolateral Cl-/base exchange activity. In comparison to studies performed with a 0 mM Cl- 0 mM HCO3- luminal solution, the use of a 0 mM Cl-, 25 mM HCO3- luminal solution inhibited both the identification and the magnitude of B cell basolateral Cl-/base exchange activity. When CCD from the inner and outer cortex were separately studied, only 7% of outer CCD intercalated cells were A cells, whereas 93% were B cells. In contrast, in the inner CCD, 58% of intercalated cells were A cells and 42% were B cells. Under stop-flow conditions, outer CCD alkalinized the luminal fluid, whereas inner CCD acidified the luminal fluid. These results indicate that all CCD intercalated cells possess basolateral Cl-/base exchange activity; however, A cell and B cell basolateral Cl-/base exchange activity differs, at least in terms of sensitivity to DIDS. Furthermore, there is axial heterogeneity in both intercalated cell type and function.