Adaptation to Metabolic Alkalosis by the Turtle Urinary Bladder

Abstract

Abstract

We studied the mechanism of adaptation to metabolic alkalosis by the turtle urinary bladder in vitro. Turtles were made alkalotic by administration of oral NaHCO₃. Bladders removed from alkalotic turtles had an increased rate of HCO₃ ^- secretion in vitro as compared with that of control. H⁺ secretion, however, was not different, indicating that metabolic alkalosis selectively increases HCO₃ ^- secretion. Fluorescence microscopy was used to quantify the carbonic anhydrase cells. The total number of carbonic anhydrase cells was determined by mucosal staining of the bladder with 6-carboxyfluorescein diacetate. The number of HCO₃ ^--secreting cells (β cells) was quantified by mucosal staining with NBD-taurine and the number of H⁺-secreting cells (α cells) was calculated from the difference between the two. Metabolic alkalosis significantly increased the total number of 6-carboxyfluorescein positive cells and NBD-taurine-positive cells. The increase in the number of 6-carboxyfluorescein positive cells was totally accounted for by the increase in the NBD-taurine-positive cells without change in the number of α cells. If NBD-taurine accurately reflects the number of β cells, these studies show that the adaptation to metabolic alkalosis is mediated, at least in part, by an increase in the number of HCO₃ ^--secreting (β) cells.