SUPPRESSION OF BLEB FORMATION, LOCOMOTION, AND POLARITY OF WALKER CARCINOSARCOMA CELLS BY HYPERTONIC MEDIA CORRELATES WITH CELL-VOLUME REDUCTION BUT NOT WITH CHANGES IN THE F-ACTIN CONTENT

The putative role of cellular or solvent volume in protrusive activity and locomotion has been investigated in blebbing Walker carcinosarcom a cells using hypertonic media. Blebbing, locomotion, and cell polarit y are completely suppressed by 0.2 M sorbitol. The response occurs in two steps. In a first step, i.e. within 10 sec after the addition of s orbitol, blebbing and locomotion are inhibited and this is associated with an average cell volume reduction by 17% (corresponding to a reduc tion in solvent volume by 38%). It clearly precedes suppression of cel l polarity (pre-existing protrusions, tail) occurring in a second step within 5 to 10 min after addition of sorbitol without additional redu ction in the cell or solvent volume. The relative amount of F-actin do es not correlate with the decrease in cell volume, suppression of bleb bing, locomotion, and cell polarity. A significant decrease in the rel ative amount of F-actin is found only at volume reductions which are h igher than those required to completely suppress blebbing, locomotion, and cell polarity. F-actin staining occurs preferentially along the c ell membrane in isotonic as well as in hypertonic media. The results a re best compatible with the hypothesis that hydrostatic pressure rathe r than actin polymerization at the front is the direct force driving t he membrane forward during bleb formation. Cells with lamellipodia sho w a similar response to hypertonic media, suggesting that basically si milar mechanisms may operate in both forms of protrusions. (C) 1997 Wi ley-Liss, Inc.