title: Turtle urinary bladder: regulation of ion transport by dynamic changes in plasma membrane area.
abstract: Turtle urinary bladder possesses four ion transport processes: Na+ absorption, H+ secretion, and HCO3- secretion-Cl- absorption. Each transport process is performed by a specific epithelial cell type. Granular cells absorb Na+ but they are not sensitive to antidiuretic hormone (ADH), unlike toad bladder granular cells. alpha-Carbonic anhydrase-rich (CA) cells secrete H+ via an apical H+-adenosinetriphosphatase (ATPase). Under conditions of low CO2 tension, this active pump is contained in the limiting membranes of certain cytoplasmic vesicles. The vesicles fuse with the apical membrane, and H+ pumps are incorporated into that membrane, as physiological conditions demand increased H+ secretion. The stimulus for fusion of these vesicles with the apical membrane appears to be intracellular acidification. beta-CA cells secrete HCO3- and reabsorb Cl-, both processes driven by H+-ATPase in the basolateral membrane in series with an apical Cl- -HCO3- exchanger. Increased intracellular adenosine 3',5'-cyclic monophosphate concentration in beta-cells stimulates net HCO3- secretion and induces an electrogenic component of this flux by activating an apical Cl- channel. This activation accompanies the fusion of an intracellular tubulovesicular network with the apical membrane. The membrane of this network may contain Cl- channels.
authors.affiliation: Department of Zoology, Ohio State University, Columbus 43210.
authors.forename: D L
authors.initials: DL
authors.lastname: Stetson
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D002256:Carbonic Anhydrases / Q000378:metabolism; D002462:Cell Membrane / Q000648:ultrastructure; D006098:Granulocytes / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D007477:Ions; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D014426:Turtles / Q000033:anatomy & histology / Q000378:metabolism*; D001743:Urinary Bladder / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D001639:Bicarbonates; D007477:Ions; D006859:Hydrogen; D002256:Carbonic Anhydrases