A comparative electron microscopic study on two strains of ascites tumor cells and their sublines resistant to antitumor agents.

A fine structural analysis of ascites tumor cells in the original sensitive strain and in the subline resistant to antitumor agents was performed with the Yoshida ascites sarcoma; its subline resistant to methylbis03-chloroethyl)amine N-oxide (MBAO); ascites hepatoma AH 13; and its sublines resistant to MBAO, mitomycin C, and 6mercaptopurine (6-MP), respectively. In the sublines resistant to MBAO the endoplasmic reticulum was more scarce than in the corresponding original strain. The vor tical arrangement of the elongated endoplasmic reticulum and the annulate lamellae, which were encountered frequently in the original Yoshida ascites sarcoma, could not be detected in its MBAO-resistant subline. The Golgi complex was also simpler, and the lamellae were poorly defined in the MBAO-resistant sublines. However, no signifi cant difference was observed between the mitomycin Cor 6-MP-resistant sublines and the original strain. As to the plasma membrane, nuclei, and nucleoli, significant differences could not be detected between the resistant sublines and the corresponding original strain.