AJP - Cell Physiology, Vol 249, Issue 1 56-C62, Copyright © 1985 by American Physiological Society
NBD-taurine fluorescence as a probe of anion exchange in gallbladder epithelium
J. K. Foskett
Previous work has demonstrated that after osmotic shrinkage of Necturus
gallbladder epithelial cells, their volumes are restored to control levels
despite the continued presence of the hyperosmotic medium. It has been
proposed that activation of parallel neutral Na+-H+ and Cl--HCO-3
exchangers in the apical membrane is necessary for regulatory volume
increase. As an independent technique to determine whether and for how long
ion flux through the anion exchanger is actually enhanced by exposure to
hypertonicity, fluorescence measurements of
N-(2-aminoethylsulfonate)-7-nitrobenz-2-oxa-1,3-diazole (NBD-taurine), a
substrate of the anion exchanger in red blood cells, have been made in
intact Necturus gallbladder. The cells were loaded with the dye by
incubation. The tissue was perfused in a miniature chamber placed on the
stage of a microscope and viewed with high-magnification optics combined
with video. Fluorescence was monitored at frequent intervals with a
photomultiplier tube, and transmittance of the tissue to the laser
excitation light was monitored with a photodiode. The epithelium was
simultaneously observed with transmitted light to control for changes in
focus or lateral movement. Exposure of the tissue to a mucosal medium made
hypertonic by the addition of mannitol transiently enhanced the efflux of
NBD-taurine from the cells in approximately 70% of the tissues examined. In
the presence of the anion-exchange inhibitor
4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS, 100
microM), hypertonicity enhanced NBD-taurine efflux in only 14% of the
preparations.(ABSTRACT TRUNCATED AT 250 WORDS)
