AJP - Renal Physiology, Vol 250, Issue 1 159-F168, Copyright © 1986 by American Physiological Society
Fluorescence identifies an alkaline cell in turtle urinary bladder
M. L. Graber, T. E. Dixon, D. Coachman, K. Herring, A. Ruenes, T. Gardner and E. Pastoriza-Munoz
Intracellular pH (pHi) of turtle bladder mucosal cells was studied by the
trapped fluorescent indicator technique. Bladders efficiently accumulated
and converted 4-methylumbelliferyl acetate to its pH-sensitive derivative
4-methylumbelliferone (4MU). Excited at the pH-indifferent wavelength 334
nm, bladders fluoresced a uniform blue. Using pH-sensitive 365-nm
excitation, 10-20% of the mucosal cells fluoresced distinctly brighter,
suggesting a more alkaline pHi. Using the 365/334 ratio to quantitate pHi,
this difference averaged 0.1 pH units. Bright cells were more distinct
after SITS or acetazolamide but disappeared after digitonin
permeabilization, dinitrophenol, or treatment with propionate, DMO, and
NH4Cl. Essentially the same population of bright cells was identified by
carboxyfluorescein diacetate. The brighter cell corresponded exactly to a
population of cells with distinctive acridine orange staining and bright
costaining with the potential-sensing probes Di-O-C5, Di-S-C3, and
4-Di-5-Asp. Two extremes of bright cell shape were seen: an elongate cell,
prevalent under conditions stimulating H+ secretion, and a more compact
cell, when acidification was inhibited. These observations support the
hypothesis that acidification represents H+ secretion via the luminal
membrane and that a primary role of carbonic anhydrase in this process is
to support the exit of base from the cell. The more alkaline cells appear
to be the carbonic anhydrase-rich cells. These cells are chemically
isolated from the surrounding granular cells and change their morphology in
response to changes in acidification. These special properties indicate a
unique role for the carbonic anhydrase cell in H+ secretion.
