Model System of Exocytotic Release in Mast Cells That Cause Allergic Responses

Exocytosis is a key process to secrete bioactive substances from cells, such as neurotransimitters, hormones, and inflammatory mediators from immune cells. Mast cells are typical non-neuronal secretory cells and secrete inflammatory mediators such as histamine and cause allergic responses. It has been shown that SNARE (soluble N-ethyl maleimide-sensitive factor attachment protein receptor) proteins play an essential role in exocytotic release in both neuronal cells and non-neuronal secretory cells. To mimic the exocytotic processes in mast cells, we developed an artificial membrane fusion system using liposomes that contains SNARE proteins. To prepare liposomes that contain SNARE proteins, SNARE proteins expressed in E. coli were purified and reconstituted into liposomes by solubilization-reconstitution methods using octylglucoside as a detergent. The membrane fusion is monitored by FRET (fluorescent resonance energy transfer) between fluorescence labeled phospholipids in liposomes (NBD- and rhodamine- labeled phospholipids). Using this assay system, we found that SNAP23, syntaxin 3 and VAMP8 are involved in exocytotic release in mast cells.