Identification of the bicarbonate secretory cell of the turtle bladder

The turtle bladder consists primarily of two mucosal cell types, mitochondrial rich (MR) and granular (G) cells. The MR cells secrete H+. In addition, the bladder secretes HCO3-, an energy-requiring Cl(-)-dependent transport system. These studies were designed to identify the cell type responsible for HCO3- secretion. Specific HCO3- and H+ secretory inhibitors were added to alter O2 consumption of MR and G cells. Cells were separated by Ficoll density centrifugation. Ouabain (10(-4) M) was used in all studies to eliminate O2 consumption associated with Na+ transport. O2 consumption of cells treated with 10(-4) M 4-acetamido-4'-isothiocyanostilbene-2,2'-sulfonic acid (SITS), which indirectly inhibits H+ secretion, was compared with cells additionally treated with 5 X 10(-4) M acetazolamide, an inhibitor of both H+ and HCO3- secretion. O2 consumption of MR cells treated with SITS alone was significantly greater than that of MR cells additionally treated with acetazolamide (delta = 0.56 +/- 0.10 microliter O2 X h-1 X mg protein-1, n = 6, P less than 0.003). There was no significant difference in G cells similarly treated. Another means of selectively altering H+ and HCO3- transports and their associated metabolic rates is to manipulate the Cl- concentration of the incubation medium. In a Cl(-)-rich medium, HCO3- and H+ transports are maximized. In low Cl(-)-SO2-4 medium, HCO3- secretion is selectively reduced.(ABSTRACT TRUNCATED AT 250 WORDS)