Levels and Distribution of the Calcium‐Modulated Proteins S100 and Calmodulin in Rat C6 Glioma Cells

To understand better the mechanisms involved in the transduction of a calcium signal into an intracellular response via multiple calcium‐modulated proteins, we have examined the calcium‐modulated proteins, S100 and calmodulin, and their intracellular targets in rat C6 glioma cells. Subconfluent, confluent, and postconfluent C6 cells contain predominantly, if not exclusively, the S100β polypeptide. The level of S100β in C6 cells increases approximately 20‐fold from subconfluency to postconfluency whereas the level of calmodulin increases only about twofold. The subcellular distribution of S100β and calmodulin in mitotic cells is similar. However, the subcellular distribution of these proteins in interphase cells is different and appears to change with cell density. Gel overlay analysis demonstrated that the S100– and calmodulin‐binding protein profiles are significantly different and that some of the binding proteins appear to change in intensity with cell density. These data demonstrate that S100β is the predominant S100 polypeptide in C6 cells and suggest that changes in S100β and S100β‐binding proteins may be involved in regulating S100‐mediated intracellular processes in C6 cells. Our studies also suggest that the levels of S100 and calmodulin may be differentially regulated in C6 cells.