Calpain Activation by Ca²⁺ and Its Role in Phagocytosis

Although the cytosolic Ca²⁺ signalling event in phagocytosis is well established, and the mechanism for generating such signals also understood, the target for the Ca²⁺ signal and how this relates to the phagocytic outcome is less clear. In this chapter, we present the evidence for a role of the Ca²⁺ activated protease, calpain, in phagocytosis. The abundant evidence for Ca²⁺ changes and calpain activation during cell shape changes is extended to include the specific cell shape change which accompanies phagocytosis. The discussion therefore includes a brief description of the domain structure of calpain and their functions. Also the mechanism by which calpain activation is limited at the cell periphery subdomains, and how this would allow phagocytic pseudopodia to form locally.