Chromosome displacement and spindle tubule polymerization. 2. Effect of alterations of extracellular calcium on displacement parameters.

Human lymphocytes were grown for either the entire culture period of 72 h or the final 6 h of culture, in media with different concentrations of calcium. Cultures were harvested without colchicine or hypotonic treatment and 'displaced' chromosomes were analysed. Long or short term exposure to various concentrations of calcium gave similar results. The frequency of cells showing displacement and the median number of displaced chromosomes per cell were highly correlated with calcium concentration (r = 1). Only the smaller chromosomes, 13-22, showed a significant correlation for displacement rate and calcium concentration. Individual chromosomes showed a consistent response to calcium which appeared to be specific for each chromosome. Chromosome 17 was the most sensitive to calcium, but chromosomes 16, 19 and most C-group chromosomes showed no response. The acrocentric chromosomes 13, 14, 15, 21 and 22 all showed a modest but similar response. An hypothesis is advanced that these responses may be controlled by specific amounts of microtubular associated proteins and/or calmodulin in the spindle tubules attached to the different chromosomes.