The fine structure of three-dimensional colonies of human glioma cells in agarose culture.

The fine structure of human glioma cells cultivated as three-dimensional colonies in agarose was investigated during exponential growth. The colonies did not show central degeneration, although they reached diameters of up to 600 mum. Large extra-cellular spaces extended throughout the colonies. The mean volumetric fraction of the spaces increased from about 20 per cent at the periphery up to nearly 40 per cent in the central regions. The quotient between nuclei and cytoplasm showed a slight decrease with depth. A proliferative gradient existed in the colonies, i.e. the mitotic index decreased almost exponentially with the distance from the surface. The distance at which the mitotic index changes by a factor of 2 was about 90 mum, corresponding to nearly five cell diameters. Cytoplasmic extensions, with a ruffling-like appearance, occurred both at the periphery and in the centre of the colonies but were larger and more frequent at the periphery. The fractions of mitochondria and vacuoles in the cytoplasm showed rather large local variations. However, the mean number of mitochondria decreased somewhat towards the centre and the number of vacuoles containing highly electron-absorbing substance increased in the most central regions.