COLOCALIZATION OF H+-ATPASE AND BAND-3 ANION-EXCHANGER IN RABBIT COLLECTING DUCT INTERCALATED CELLS

Two major types of intercalated cells (IC) have been previously defined in rabbit collecting duct: alpha-cells have a basolateral band 3-like anion exchanger and secrete H+, whereas beta-cells bind peanut agglutinin (PNA) apically and are believed to secrete HCO3-. To further define IC types, we double-labeled kidney sections with anti-H+-ATPase antibodies and with either an anti-band 3 antibody or PNA. We found four patterns of staining: 1) IC with apical H+-ATPase and basal band 3, a configuration consistent with ongoing H+ secretion, which prevailed in the inner stripe of outer medulla (OMCD(i)); 2) diffuse H+-ATPase labeling across the cell and basal band 3, which was most numerous in the outer stripe of outer medulla (OMCD(o)); 3) IC with "bright" apical peanut lectin, diffuse H+-ATPase, and no band 3, which was abundant in the cortical collecting duct (CCD) and probably represents HCO3--secreting cells; and 4) "hybrid" cells with various staining combinations (e.g., apical lectin binding and apical H+-ATPase), which although they are uncommon, were seen in the CCD. Consistent with this immunocytochemical finding of hybrid cells, cell-sorting studies on isolated CCD IC showed that 6-18% of PNA-positive cells also stained positively for band 3. We conclude that 1) band 3-positive IC in the OMCD vary axially. Most OMCD(i) IC are probably active proton secretors, whereas up to one-half of OMCD(o) IC may be latent H+ secretors. 2) The diffuse H+-ATPase pattern in putative beta-cells differs from comparable results in the rat and is not consistent with a "reversed" alpha-cell. HCO3- secretion by beta-cells may be driven by an H+ extrusion mechanism other than the alpha-cell pump re-sorted to the basolateral membrane. 3) The possibility of hybrid cells that might combine alpha- and beta-cell transport proteins suggests a mechanism for functional reversal of collecting duct IC polarity.