• cell fusion;
  • cell morphology;
  • endocytosis;
  • active oxygen species

Fused Ehlrich ascites tumor (EAT) cells induced by hemagglutinating virus of Japan (HVJ; Sendai virus) had an irregular shape, reflecting the shape of cell aggregates before fusion. During subsequent culture, the fused cells gradually took on a spherical form within 60min. Examination of the fused cells revealed a vigorous endocytosis of the cell membrane during the morphological change. When EAT cells were treated with porphyrin derivatives, and the morphological change to a spherical form was inhibited, endocytosis of fused cells was also suppressed, suggesting that the change is closely associated with endocytotic activity. Further examination with porphyrin derivatives and hydrogen peroxide suggested that the inhibition of morphological change is due to the suppression of endocytosis by active oxygen species produced by these substances. Experiments using an endocytotic inhibitor, methylamine, indicated that endocytosis is essential for the morphological change that occurs in the fused cells.