FcεRI cross‐linking‐induced actin assembly mediates calcium signalling in RBL‐2H3 mast cells

To determine the role of actin assembly in the Ca 2+ signalling of mast cells activated by cross‐linking of FcεRI, we examined the effects of cytochalasin D, an inhibitor of actin polymerization. In the RBL‐2H3 cells, F‐actin content was increased by sensitization with anti‐dinitrophenol (DNP) IgE. In these cells, cytochalasin D induced oscillatory increases in cytosolic Ca 2+ ([Ca 2+ ] i ); these increase were inhibited by jasplakinolide, a stabilizer of actin filaments. In the IgE‐sensitized RBL‐2H3 cells, DNP‐human serum albumin (DNP‐HSA) augmented actin assembly. DNP‐HSA also increased the production of IP 3 , [Ca 2+ ] i and degranulation. Cytochalasin D enhanced all of these DNP‐HSA‐induced effects. In a Ca 2+ ‐free solution, DNP‐HSA induced a transient increase in [Ca 2+ ] i , and this increase was accelerated by cytochalasin D. After cessation of the DNP‐HSA‐induced Ca 2+ release, the re‐addition of Ca 2+ induced a sustained increase in [Ca 2+ ] i through capacitative Ca 2+ entry (CCE), and this increase was enhanced by cytochalasin D. The effect of cytochalasin D in enhancing the CCE activity was prevented by xestospongin C. In contrast, neither the Ca 2+ release nor the CCE activation that was induced by thapsigargin was affected by cytochalasin D. These results suggest that actin de‐polymerization stimulates the FcεRI‐mediated signalling to augment the release of Ca 2+ from the endoplasmic reticulum in RBL‐2H3 cells.British Journal of Pharmacology (2002) 136 , 837–846. doi: 10.1038/sj.bjp.0704788