Fig. 3. Inverse correlation between extent of morphological response of quiescent R22 cells to cytoskeletal disruption and PAI-1 transcript abundance. Cells maintained under serum-free culture conditions for 3 days were generally well spread with little membrane ruffling (A). A 4 hour exposure to 10 µM CD resulted in an arborized phenotype (B), although the cellular periphery remained well demarcated and easily visible for footprint imaging. Colchicine exposure (10 µM, 4 hours) (C) did not produce the same arborized effect as CD, although the cellular footprint area was similarly reduced (by 35%) in CD- and colchicine-treated cultures. Computerized imaging was done on 75 randomly selected individual cells per culture condition in three sets of 25 cells each. The footprint area was significantly reduced by treatment with either drug at the maximal PAI-1 transcript-inducing concentration of 10 µM (Fig. 4). Comparison between DMSO and CD-treated cells indicated an approximate reciprocal relationship between cellular footprint area and PAI-1 expression (D). The histogram in (D) illustrates the mean±s.d. (in arbitrary units) for triplicate determinations of footprint area and PAI-1 levels.