The use of a new fluorescent viscosity indicator to study the relationship between transmembrane potential and...

A new fluorescent dye, polymethine derivative 4501 U, was applied to label the cytoplasmic membrane of mouse lymphocytes to investigate whether the membrane lipid dynamics is related to the transmembrane potential. The dye was found not to alter the cell viability. The dye is localized close to the external surface of the membrane, and its spectroscopic characteristics make it possible to obtain information on membrane fluidity using the intensity ratio of its two emission peaks. In contrast to recent data indicating that transmembrane potential alters the membrane lipid dynamics (as revealed by anisotropy studies with diphenyl hexatriene) 4501 U does not show such a relationship. The investigations presented support the hypothesis that the change in the transmembrane potential affects the dynamics/structure of the membrane region only at the interface between the two lipid layers.