AJP - Cell Physiology, Vol 252, Issue 5 C570-C574, Copyright © 1987 by American Physiological Society
Band 3 is the basolateral anion exchanger of dark epithelial cells of turtle urinary bladder
D. Drenckhahn, M. Oelmann, P. Schaaf, M. Wagner and S. Wagner
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.
