AJP - Lung Cellular and Molecular Physiology, Vol 269, Issue 1 78-L84, Copyright © 1995 by American Physiological Society
Reduction of thiazine dyes by bovine pulmonary arterial endothelial cells in culture
R. D. Bongard, M. P. Merker, R. Shundo, Y. Okamoto, D. L. Roerig, J. H. Linehan and C. A. Dawson
Department of Physiology, Medical College of Wisconsin, Milwaukee 53226, USA.
The uptake of methylene blue (MB), and toluidine blue O (TBO) by bovine
pulmonary arterial endothelial cells grown on microcarrier beads was
detected as a decrease in the concentration of dye in the medium after
these thiazine dyes were added to the medium surrounding the cells. Because
the reduced forms of these dyes are much more lipophilic than the oxidized
forms, we considered the possibility that reduction of the dyes at the cell
surface might have preceded the uptake by the cells. Therefore, we studied
the ability of the cells to reduce a toluidine blue O-polyacrylamide
polymer (TBOP), which was too large to enter the cells in either the
oxidized or reduced form. The TBO moieties of the polymer were reduced by
the cells, indicating that the dyes did not have to enter the cells to be
reduced and that reduction can occur at, or near, the cell surface. The
rate of TBOP reduction was about the same as the rate of uptake of the
monomeric dyes, indicating that the cell surface reduction mechanism had a
sufficient capacity to account for the monomer uptake by the cells. We also
found that ferricyanide ion, which also did not permeate the cells, was
reduced by the cells and that external ferricyanide inhibited the monomeric
MB uptake. Thus the results with ferricyanide were also consistent with the
concept that the monomeric thiazine dyes are reduced at the cell surface
before the more lipophilic reduced forms are taken up by the endothelial
cells.
