Frequency distribution histograms of oxygen tensions in multicell spheroids.

Recessed oxygen sensitive microelectrodes have been used to measure oxygen tensions in spheroids from EMT6/Ro mouse mammary carcinoma cells and from V-79-171B hamster lung fibroblasts. During the experiments the spheroids were exposed to conditions similar to those prevailing during growth and previous experiments with radiation and/or drugs. Frequency distribution curves were generated from 386 steady state readings in EMT6 (N = 20) spheroids with diameters ranging from 386 to 1900 micron and from 289 steady state readings in V79 spheroids (N = 20) with diameters between 376 and 1052 micron. Small spheroids exhibit higher pO2 values than spheroids of medium and large size. Oxygen tensions in small and medium size V79 spheroids are lower than in EMT6 spheroids of the equivalent size ranges. The pO2 histograms in large spheroids of both cell types are similar to pO2 frequency distributions in solid tumors. It is concluded that spheroids may represent a valuable model to provide evidence for the way pO2 histograms are influenced by the density of capillaries, by the cellular O2 consumption and by the sampling technique.