[Formation of processes during fibroblast spreading in an in vitro medium with cytochalasin B]

The spreading of normal mouse fibroblasts in a solid substrate involves extension and attachment of numerous pseudopodia resulting in the formation of lamellar cytoplasm in the cell periphery which is attached to the substrate. During the spreading of fibroblasts in the presence of cytochalasin B (CB), a system of arbor-like branched processes forms de novo, rather than lamellar cytoplasm. Unlike the normal lamellar cytoplasm, the arbor-like processes are unable to clear their surface from concanavalin A-patched receptors and do not reveal microfilament bundles in their attachment sites. The cells spreading in the presence of both CB and colcemid do not form well-organized branched structures but extend numerous unstable pseudopodia. The formation of lamellar cytoplasm can be regarded as a combination of several functionally different processes: a) rudimentary pseudopodial CB- and colcemid-resistant reactions, b) CB-sensitive lamelliation, and c) colcemid-sensitive stabilization.