title: Band 3 is the basolateral anion exchanger of dark epithelial cells of turtle urinary bladder.
abstract: The turtle urinary bladder serves as a model for collecting duct functions in the mammalian kidney. The epithelium of both the turtle bladder and the mammalian collecting duct can generate a steep gradient for H+ ions between blood and urine. Secretion of H+ into the urine is coupled to a basolateral efflux of HCO-3 that appears to be exchanged mainly against Cl-. Here we show that approximately 80% of the dark cells of the bladder contain a 110,000 relative molecular weight (Mr) analogue of the turtle erythrocyte anion exchanger, band 3. The band 3 analogue is confined to the basolateral cell surface and is absent from the apical membrane. A minor population of the dark cells (approximately 20%), which have been previously suggested to represent reverse cells that are involved in HCO-3 secretion rather than absorption, appears not to express a band 3-like anion exchanger, at either the apical or the basolateral membrane. The bladder band 3 protein is colocalized with actin and isoforms of ankyrin (200,000 Mr) and spectrin (230,000 Mr) along the basolateral membrane. Linkage of band 3 via ankyrin to the spectrin-actin lattice may restrict this anion exchanger to the basolateral membrane surface. In view of our previous observation of a band 3-like anion exchanger in the collecting duct epithelium of the rat kidney, these findings point to a common molecular basis for acid-base transport in the mammalian collecting duct and the reptilian urinary bladder.
mesh_terms: D000818:Animals; D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D000838:Anions / Q000378:metabolism*; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D007474:Ion Exchange; D014426:Turtles; D001743:Urinary Bladder / Q000166:cytology / Q000378:metabolism*
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D000838:Anions