The effect of external stimuli on rat middle ear epithelium in culture. Extracellular carbon dioxide concentration.

Serially cultivated rat middle ear epithelium was studied under exposure to various concentrations of carbon dioxide. Three experiments were performed exposing the epithelium to a gaseous environment containing 5 or 10% CO2 or to an atmosphere almost devoid of CO2. Oxygen was maintained constant at 20% and nitrogen was additionally supplied. Cells exposed at 0% CO2 showed a remarkably different morphology compared with the cultures at 5 and 10% CO2, cells could become extremely large at 0% CO2, also showing a great variation in shape and cell size within the culture. Proliferation was significantly impaired at 0% CO2 vis-à-vis the 5 and 10% experiments. Terminal differentiation, however, was not influenced by the different CO2 concentrations, indicating that in vitro, variation in CO2 concentration is of no importance regarding a possible differentiation of middle ear epithelium into a cornifying epithelium.