Surface characteristics of carbonic-anhydrase-rich cells in turtle urinary bladder

Addition of a disulfonic stilbene, 4-acetamido 4'-isothiocyano-2,2'-disulfonic stilbene (SITS), to the serosal side of the turtle bladder blocks the efflux of bicarbonate ions from the acidifying cells and thereby inhibits hydrogen ion secretion into the luminal solution. Because SITS has little effect on other transport systems, we used it to define the relationship between hydrogen ion secretion (JH) and the different cell types facing the luminal surface. Cells were identified by scanning and transmission electron microscopy (SEM and TEM) and by histochemical localization of carbonic anhydrase (CA). SEM revealed that SITS caused marked alterations in luminal surface characteristics of a cell population with prominent microplicae. Two hours after the serosal addition of SITS, cells with identifiable microplicae had decreased from 12.7 to 0.5% of total cells. TEM studies and CA histochemistry showed that the number of cells rich in CA (CA cells) remained the same, whereas the individual luminal surface areas of a subpopulation of CA cells had decreased markedly. A comparison of the distribution of individual surface areas of cells with microplicae and CA cells revealed that the CA cells with large surface areas corresponded to the cells with microplicae and that both were affected by the serosal addition of SITS. Acetazolamide, which also inhibits JH, caused similar changes. The luminal addition of SITS and an inactive analogue of acetazolamide, which have no effect on JH, did not alter surface morphology, These results indicate that the CA cell with microplicae represents the active state of the hydrogen ion secreting cell.