Actin rearrangement in living cells revealed by microinjection of a fluorescent phalloidin derivative.

A fluorescent derivative of phalloidin with a high affinity for F-actin was microinjected into tissue culture cells and its intracellular reorganization was followed by TV image intensification and video recording. When the F-actin stabilizing drug is used at concentrations, which do not inhibit cellular movement, rearrangement of fluorescently labelled microfilament bundles can be followed directly. We discuss the possibility that active ruffles are governed by structural rules different from those applying to stress fibers and raise the possibility that actin may be released from microfilaments in a form different from G-actin.