Changes in O2 consumption of multicellular spheroids during development of necrosis.

Using O2-sensitive microelectrodes oxygen tension profiles were recorded in EMT6-spheroids either showing no necrosis or having developed a small necrotic area in the center. The profiles obtained were in accordance with those measured in previous investigations under similar conditions. The volume-related O2-consumption rate Q in the viable parts of the spheroids could be determined through theoretical considerations. The results show that there is a steep decrease in Q by a factor of three when the spheroids grow from diameters of 200 micron to diameters larger than 1000 micron. The drop in Q mainly occurs in a size range in which central necrosis develops in EMT6-spheroids cultured under these particular conditions. Among other factors, changes in the proliferative status, in extracellular volume fraction or in physiological parameters of the micromilieu in spheroids, such as accumulation of metabolic waste products or of toxic substances from the necrotic area may contribute to the variation in Q observed.