  The aims of the current study were to establish a system of culture for
induction of paralysed chondrocytes and to investigate if these cells are
really dying. Chondrocytes were isolated from the growth cartilage of fetal
equines, centrifuged and cultured as pellets in either 10% fetal calf serum or
10% horse serum for 28 days and processed for light and electron microscopy.
Different cell types were counted and expressed as a percentage to the total
cell number. Growth kinetics including the pellet weight and thickness and the
cellular density were evaluated. After 7 days in culture, paralysed
chondrocytes with similar morphology to those described in the rabbit growth
cartilage could be identified in pellets in each serum type, however, the
proportion of the cells was different. In pellet cultured with 10% fetal calf
serum, more than 50% of the cells were paralysed chondrocytes but in 10% horse
serum, less than 10% of cells were of paralysed type. At day 14, about 50% of
the cells in pellets cultured in either serum type differentiated into
hypertrophic dark chondrocytes and the proportion of paralysed cells was
markedly decreased. After 21 days in each culture, more than 70% of the cells
were hypertrophic dark chondrocytes and no paralysed chondrocytes could be
observed. The paralysed chondrocytes may be not dying and they likely to be an
immature form of hypertrophic dark chondrocytes. It is better to use the term
immature dark chondrocytes instead of paralysed cells. This culture system will
be useful for further molecular studies on paralysed chondrocytes and to
explore the functions of these cells.
