Postnatal maturation of rabbit renal collecting duct III. Peanut lectin-binding intercalated cells

Measurements of transepithelial HCO³ transport in the rabbit cortical collecting duct (CCD) indicate that net HCO₃ secretion becomes apparent only after the first month of life [F. M. Mehrgut, L. M. Satlin, and G. J. Schwartz, Am. J. Physiol. 259 (Renal Fluid Electrolyte Physiol. 28): F801-F808, 1990]. We used fluorescent probes and immunocytochemistry to trace the postnatal functional development of the β-intercalated cell, the HC0₃-secreting cell of the fully differentiated CCD. Throughout maturation, the β-intercalated cell was empirically identified by its selective uptake of the pH-sensitive dye 2′ ,7′ (carboxyethyl)-5(6)-carboxyfluorescein, an alkaline cell pH, apical binding to peanut agglutinin (PNA) and monoclonal antibody B63, and by its functional capacity for apical Cl-HCO₃ exchange as manifested by Cl-dependent extrusion of an intracellular alkali load. Compared with the mature segment, the neonatal mid-CCD exhibited fewer intercalated cells, which were characterized by a less alkaline cell pH, reduced apical Cl-HCO₃ exchange activity, and shorter apical binding profiles for PNA. There was evidence for basolateral Cl conductance and similar buffering capacity at all ages. In the neonatal outer cortex there was little or no binding to PNA or to B63. As soon as cell surface antigens characteristic of the fully differentiated β-cell were detected, functional studies indicated the presence, albeit reduced, of apical Cl-HCO₃ exchange. Thus there is postnatal proliferation and maturation of HCO₃-secreting intercalated cells in the rabbit kidney; the origin of these cells remains to be determined.