Differences in calmodulin levels of normal and transformed cells as determined by culture conditions.

Several studies have suggested that calmodulin (CAM) levels increase in cells as a consequence of transformation by RNA tumor viruses. This study examines factors affecting CAM levels in normal and transformed chick embryo fibroblasts. Significant differences in CAM levels of normal and transformed cells were observed as cells grew from subconfluent to confluent densities. These changes were not cell cycle dependent, nor did they correlate with the growth rate of the cultures. The most significant difference between normal and transformed cultures was a lack of down-regulation of CAM levels in transformed cells as compared to normal chick embryo fibroblasts. This decrease in CAM levels in normal cells occurred in high density cultures that were allowed to grow undisturbed for several days without trypsinization and reseeding. These experiments do not support the contention that differences in the growth potential of cycling cultures of normal and transformed cells are regulated through modulation of CAM levels.