New fluorescent probes for the measurement of cell membrane viscosity

Background: Molecular rotors are fluorescent molecules that exhibit viscosi ty-dependent fluorescence quantum yield, potentially allowing direct measur ements of cell membrane viscosity in cultured cells. Commercially available rotors, however, stain not only the cell membrane, but also bind to tubuli n and migrate into the cytoplasm. We synthesized molecules related to 9-(di cyanovinyl)-julolidine (DCVJ), which featured hydrocarbon chains of differe nt length to increase membrane compatibility. Results: Longer hydrocarbon chains attached to the fluorescent rotor reduce the migration of the dye into the cytoplasm and internal compartments of t he cell. The amplitude of the fluorescence response to fluid shear stress, known to decrease membrane viscosity, is significantly higher than the resp onse obtained from DCVJ. Notably a farnesyl chain showed a more than 20-fol d amplitude over DCVJ and allowed detection of membrane viscosity changes a t markedly lower shear stresses. Conclusions: The modification of molecular rotors towards increased cell me mbrane association provides a new research tool for membrane viscosity meas urements. The use of these rotors complements established methods such as f luorescence recovery after photobleaching with its limited spatial and temp oral resolution and fluorescence anisotropy, which has low sensitivity and may be subject to other effects such as deformation. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.