Localization of transport compartments in turtle urinary bladder

Abstract

To characterize different transport compartments in the urinary bladder epithelium of postabsorptive turtles, the electrolyte composition of individual cells was determined using electron microprobe analysis. After blocking the transepithelial Na transport, the short-circuit current decreased from positive to negative values (from 26.5 +/- 17.7 to -3.9 +/- 2.9 after ouabain and from 25.4 +/- 17.2 to -8.0 +/- 5.1 microA/cm2 after amiloride). Whereas under control conditions the Na and K concentrations were similar in all cell types and the same was true for Cl in most of the cells, some cells exhibited very low Cl concentrations. The epithelial cells were subdivided according to their electrolyte composition into ouabain-sensitive and ouabain-insensitive ones. In the ouabain-sensitive cells, which made up the majority of epithelial cells and showed a relatively high Cl concentration (about 36 mmol/kg wet weight), the Na concentration increased after ouabain by about 90 mmol/kg wet weight and the K concentration decreased by a similar amount. Since these alterations could largely be prevented when amiloride was applied before ouabain, it is suggested that the granular and basal cells form a syncytial Na transport compartment similar to that in other multilayered epithelia. The ouabain-insensitive cells, in which almost no alteration in Na and K concentrations was observed after ouabain, were subdivided into a Cl-rich (34.6 +/- 7.6 mmol/kg wet weight) and a Cl-poor (12.0 +/- 5.6 mmol/kg wet weight) population. Since in these cells no large mucin granules were detectable, they are regarded as carbonic anhydrase-rich cells involved in H and HCO3 transport.

Na Transport in Rat Gastric Mucosa: An Electron Microprobe Analysis

“…Whereas the concentrations of Na, K and Cl typically located in the free cyto plasm were much smaller than in basal cell areas, S and Ca concentrations were much higher. Similar element compositions were observed in other mucin granule-containing epithelial cells such as the goblet cells of the colon [14] and the toad urinary bladder [15] and the granular cells of the turtle urinary bladder [16], Whereas in about 85% of upper and lower gland cells the Na concentration was very homogeneous and only 10 mmol/kg ww, it was variable and about 40 mmol/kg ww high er in the remaining cells. Whether the differ ent Na concentrations belong to different cell types, or whether the high Na concentration in some of the cells reflects beginning cell death cannot be answered by the present study.…”

Electroneutral Acid Secretion in Frog Gastric Mucosa: An Electron Microprobe Analysis

“…This element composi tion, which differs considerably from that in basal cell regions, might be caused by the mucus located within large apical mucin gran ules. Similar element compositions have been observed for other mucin granule-containing epithelial cells [20,23]. Compared with the present data, chemical analysis has yielded higher intracellular Na and Cl and lower K concentrations [24], The reason for this dis crepancy might be that the radioiodinated se rum albumin, used as extracellular space marker in the chemical analysis, does not assess the extracellular space completely, meaning that a fraction of the extracellular space (high Na and Cl and low K concentra tions) is falsely regarded as cellular.…”

Identification of Acid-Base-Secreting Cells in Turtle Urinary Bladder by the Cellular Uptake of Br^-

“…The treatment of the animals prior to the experiments, dissection of the bladders, and incu bation of isolated bladder pieces in Ussing-type cham bers (exposed area 0.75 cm2) were similar to previously described procedures [3]. Because the animals were not fed during the 7 days prior to the experiments they can be regarded as 'postabsorptive'.…”

“…The epithelium of the turtle urinary blad der consists of three different cell types, granular, basal, and carbonic-anhydrase-rich (CA) cells [1,2], Whereas granular and basal cells probably form a syncytial transport compart ment [3] involved in Na+ absorption [3][4][5], the CA cells seem to be responsible for acid-base secretion and Cl-absorption [6], Ultrastructural investigations have demonstrated that H+ secretion is performed by a-type, and HCO3 secretion by (3-tvpe CA cells [7]. Sev eral lines of evidence indicate that the mem brane transporters primarily involved in acid and ordinary base secretion are an H+ translo cating ATPase and an anion exchanger [8.…”

“…Electron microprobe analysis has shown that CA cells, in contrast to granular and basal cells, do not respond to ouabain with large alterations in their intracellular Na+ and K+ concentrations, and that CA cells could be subdivided into a CP-rich and a CP-poor sub population [3], Because the numerical rela tions between a-and (3-cell types and between CP-rich and CP-poor CA cells were almost identical, it has been suggested that the CPrich cells might be involved in HP and the CP-poor cells in HCO3 secretion [3], To test this hypothesis, the uptake of Br' into the different epithelial cell types was determined from either the luminal side un der control conditions, or from the serosal side before and after the application of either the disulfonic stilbene, SITS, or low luminal pH. The experimental rationale was based upon the observations that B r is accepted by the anion exchangers instead of CP to about 20% at the luminal [ 10] and to > 80% at the serosal side [ 11],…”