Figure 9.

Immunofluorescence labeling of actin in a control cell (A) and in cells treated with cytochalasin D alone (B), staurosporine alone (C), or staurosporine plus cytochalasin D sequentially (D). Cytochalasin D alone stops flow and produces a buildup of actin at the cell margin along with an actomyosin-mediated contraction of the cytoskeleton, leaving an actin-free peripheral zone. Staurosporine, a broad-spectrum kinase inhibitor that can inhibit MLCK, stops flow and disrupts the actin organization in the cell center; however, flow continues unabated at the cell periphery (C). Sequential treatment with staurosporine followed by cytochalasin D arrests flow and causes an accumulation of actin staining at the cell edge. However, the cytoskeleton does not undergo a retraction, suggesting that the kinase inhibitor is indeed inhibiting MLCK function and thereby reducing the actomyosin-mediated tension on the cytoskeleton. Bar, 10 μm.