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Fig. 3. Taxol-induced polymerization of microtubules does not prevent receptor sequestration in response to stimulation. A431 cells stably expressing GFP-tagged ß₂AR (A) or wild-type (B) were stimulated with either insulin or isoproterenol for 30 minutes. Taxol (10 µM, (`+Taxol(') was added to cells for 30 minutes in advance. (A) GFP-tagged ß₂AR internalization following stimulation was fixed and analyzed by confocal microscopy (control, upper panel). Pretreatment with taxol (lower panel) does not significantly affect receptor internalization in stimulated cells. (B) The same experiment performed on wild-type A431 cells: fixed (2% paraformaldehyde in PBS, pH 7.2) wild-type cells were immunostained with monoclonal antibodies against ${alpha}$ -tubulin coupled with FITC. Images from confocal microscopy showed the typical pattern of microtubules cytoskeleton in A431 cells (control experiment, upper panel). Treatment with taxol (lower panel) induced its polymerization and redistribution. Polymerized microtubules formed bulky rigid structures, localized in the cell periphery, in a parallel manner to the plasma membrane. Additional stimulation with isoproterenol ((`+Iso(') counteracts the effects of taxol and restores the arrangement of microtubules, radiating from nuclear vicinity with microtubules forming prominent arrays. Bars, 10 µm. ß₂ARs localized either to the cell membrane (yellow arrows) or to the intracellular space (white arrowheads).

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