TRANSIENT CYTOPLASMIC VACUOLIZATION IN CULTURED NORMAL AND NEOPLASTIC-CELLS TREATED WITH LOW-MOLECULAR-WEIGHT HUMAN SERUM ULTRAFILTRATE - IS OUT INSIDE

Human embryonal fibroblasts (HEF) and epithelial carcinoma cells (HEp- 2) were exposed to low molecular weight (LMW) fractions (M(R) < 50-kDa ) of human serum, generated by ultrafiltration. A prominent change in cytoplasmic morphology was detected by microscopic analysis of both ce ll types. Within 1-3 h of incubation an extensive vacuolization was in duced, which phenotype was maintained for 6-12 h in the presence of th e LMW filtrate in a cell type dependent manner, followed by a spontane ous reconstitution of the original cytoplasmic morphology by 24 h. Rev ersibility occurred by incubation in medium without filtered serum fra ctions. Transmission electron microscopy revealed vesicles without con tinuous bordering membrane or electron dense interna and demonstrated vacuoles in close contact with filamentous structures. Taken together the light- and electron microscopic characteristics of the observed va cuolization, potential interpretations of our results are discussed in the context of general cytoplasmic organization. Rearrangement of the cytoplasmic protein-water system as a consequence of an inductive eff ect of serum filtrates is proposed.