Increased content of calmodulin in human leukemia cells.

The content of calmodulin, as measured by a radioimmunoassay, in homogenates of two human leukemic cell lines (IM9 and Molt-4) was about 10-fold higher than that of normal human peripheral lymphocytes. These elevated calmodulin levels existed regardless of the proliferation status of the cells. Normal human lymphocytes stimulated with concanavalin A (con A) did not exhibit these elevated calmodulin levels. Likewise, leukemic cells which were 'blocked' from dividing through the addition of thymidine did not exhibit lower or 'normal' cellular calmodulin levels. These increased levels of calmodulin could contribute to the altered calcium regulation which exists in human leukemic lymphocytes.