CUTTING EDGE - CA2-DEPENDENT EXOCYTOSIS IN MAST-CELLS IS STIMULATED BY THE CA2+ SENSOR, SYNAPTOTAGMIN()

Mast cells secrete a variety of biologically active substances that me diate inflammatory responses. Synaptotagmin(s) (Syts) are a gene famil y of proteins that are implicated in the control of Ca2+-dependent exo cytosis. In the present study, we investigated the possible occurrence and functional involvement of Syt in the control of mast cell exocyto sis. Here, we demonstrate that both connective tissue type and mucosal -like mast cells express Syt-immunoreactive proteins, and that these p roteins are localized almost exclusively to their secretory granules. Furthermore, expression of Syt I, the neuronal Ca2+ sensor, in rat bas ophilic leukemia cells (RBL-2H3), a tumor analogue of mucosal mast cel ls, resulted in prominent potentiation and acceleration of Ca2+-depend ent exocytosis. Therefore, these findings implicate Syt as a Ca2+ sens or that mediates regulated secretion in mast cells to calcium ionophor e.