Fig. 4. Effects of Rho kinase inhibitor on S1P-induced stress fibres. C2C12 myoblasts were stimulated with 1 µM S1P for 30 minutes in the absence (A) or presence of 50 µM Y-27632 (B), fixed and observed under a confocal laser microscope. Note that, after the pretreatment with the Rho kinase inhibitor, cells have only a few peripheral stress fibres and scattered focal adhesions. Time-lapse analysis of myoblasts expressing GFP-actins by two-photon excitation fluorescence microscopy (C and D). Images were taken 1 minute (C) and 30 minutes after (D) the application of 1 µM S1P. The pretreatment with the Rho kinase inhibitor causes shortening and disruption of actin filaments. The images are representative of at least three independent experiments with similar results.