Reorganization of the Actin Cytoskeleton in Human Fibroblasts Induced by PDGF and Neomycin

Abstract

Among the earliest effects on cells of platelet derived growth factor (PDGF), a growth-stimulating factor normally occurring in blood, are stimulation of lamellipodia formation and induction of changes in the actin cytoskeleton. We have investigated these phenomena by time lapse video (TLV) and fluorescence light microscopy (FLM), and high resolution scanning electron microscopy (SEM) using two strains of human diploid fibroblasts: ICIG-7 from embryonic lung and AG1523 from foreskin, grown either on coverglasses or on carbon-stabilized Formvar-coated gold electron microscope grids. Cells were maintained in serum-free culture medium for 48 hours prior to addition of PDGF (5-20 ng/ml), neomycin sulfate (0.7-7 mM), or neomycin followed by PDGF. For TLV cells were filmed continuously before, during, and after addition of experimental reagents. For FLM and SEM cells were either fixed directly in 4% paraformaldehyde or 2.5% glutaraldehyde (GA) respectively, or extracted in 0.5% Triton X-100 in microtubule stabilizing buffer (Tsb) and then fixed.