NBD-taurine uptake by alpha-type carbonic anhydrase cells of turtle bladder.
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)
Palmisano
J
J
Division of Nephrology, University of Connecticut School of Medicine, Farmington 06032.
Mitchell
P P
PP
Steinmetz
P R
PR
D000818:Animals; D001692:Biological Transport; D002256:Carbonic Anhydrases / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008856:Microscopy, Fluorescence; D010069:Oxadiazoles / Q000378:metabolism*; D013654:Taurine / Q000031:analogs & derivatives* / Q000378:metabolism; D014426:Turtles; D001743:Urinary Bladder / Q000166:cytology / Q000378:metabolism*
D005456:Fluorescent Dyes; C027027:NBD-taurine; D010069:Oxadiazoles; D013654:Taurine; D002256:Carbonic Anhydrases