AJP - Renal Physiology, Vol 257, Issue 6 1015-F1020, Copyright © 1989 by American Physiological Society
NBD-taurine uptake by alpha-type carbonic anhydrase cells of turtle bladder
J. Palmisano, P. P. Mitchell and P. R. Steinmetz
Division of Nephrology, University of Connecticut School of Medicine, Farmington 06032.
The uptake of the fluorescent anion, N-(7-nitrobenz-2-oxa-1,3
diazol-4-yl)aminoethanosulfonic acid-taurine (NBD-T) was examined in sheets
of turtle bladder epithelial cells after either serosal or mucosal exposure
to the fluorescent anion. Serosal uptake of NBD-T into a population of
epithelial cells was demonstrated in thin epithelial sheets scraped from
bladder sacs exposed to low (0.5 mM) concentrations of NBD-T sufficient to
cause fluorescence in turtle erythrocytes. In nine sheets NBD-T
fluorescence was observed in 14.4 +/- 1.3% of epithelial cells; by
phase-contrast microscopy of the same fields, these cells were nongranular
or carbonic anhydrase (CA) cells. An additional 8.1 +/- 1.0% of cells was
nongranular, but failed to exhibit fluorescence after serosal NBD-T
exposure, consistent with a beta-CA cell population. Apical uptake of NBD-T
into epithelial cells was demonstrable only at high (5 mM) mucosal
concentrations in both thin sheets and superfused bladder segments. In thin
sheets, NBD-T fluorescence was observed in 15.8 +/- 0.7% of cells and
appeared to have a punctate subapical distribution; phase-contrast of the
same fields (n = 46) revealed a nongranular cell population of 21.9 +/-
0.9%. Nongranular cells corresponded closely to CA cells as identified with
carboxyfluorescein fluorescence. Hence, apical NBD-T was taken up primarily
by alpha-CA cells. In conclusion, NBD-T is transported by alpha-CA cells
either across the basolateral membrane with high affinity comparable to
that of turtle red cell band 3 protein or across the apical membrane with
low affinity via a less-specific mechanism such as endocytosis.(ABSTRACT
TRUNCATED AT 250 WORDS)
