[Influence of serum content of the culture medium upon growth and microtubule-microfilament system of Ehrlich ascites tumor cells in monolayer culture (author's transl)].

Withdrawal of serum from the medium of monolayer cultures of the Ehrlich ascites tumor within their phase of exponential growth resulted in a nearly complete inhibition of growth during a 25-hour incubation, but cells were not dying off. In the course of this serum-free incubation no significant alteration of the cellular glycolytic rate was seen. Addition of serum to cultures which previously had been incubated without serum led to a resumption of cell proliferation. The microtubule-microfilament system of cells cultivated without serum as compared to cells cultured in presence of serum was significantly reduced concerning the number and length of microtubules as well as the diffuse, bunchy or reticular arrangement of the microfilaments. The lesser development of the microtubule-microfilament system corresponds well to the reduced pinocytosis activity (ascertained by former studies) which is caused by a lack of serum. The present experiments altogether give support to the concept that serum factors as exogenous stimuli are necessary not only for cell growth but also for the probably closely interrelated development of the microtubule-microfilament system needed e.g. for the organization of cell surface structures and activities.