The effect of cytochalasin B on the endosteal lining cells of mammalian bone. A scanning electron microscopic study.

The lining osteoblasts of the rat tibial endosteum were treated for various times (between 1 and 60 min) and increasing doses (3.87-38.7 microgram/ml) with the macrolide fungal metabolite cytochalasin B (CB). Dimethylsulfoxide (DMSO) served as the vehicle for CB and was administered to control tissues. An in vitro incubation system and scanning electron microscopy (SEM) were used to evaluate the effects of CB. The drug initiated cell rounding (contraction), nuclear protrusion, bleb formation, and the subsequent clustering of blebs and microvilli into aggregates. All CB-induced aberrations of the surface structure were readily reversible when tissues were washed with CB-free media. DMSO had no significant effect on cell surface morphology. The reversible structural changes brought about by CB are explained in terms of alterations of the subplasmalemmal cortical microfilament system of osteoblasts. The potential use of CB in evaluating the bone cell cytoskeleton and its relationship to the physiology of the cellular functional membrane (endosteum) of bone is discussed.