PARACRINE CA2-VITRO - SEROTONIN-MEDIATED CELL-CELL COMMUNICATION IN MAST-CELL SMOOTH-MUSCLE COCULTURES( SIGNALING IN)

Mast cells are tissue-resident immune cells that are capable of signal ing many different cell types in vascularized tissue including epithel ia and smooth muscle. We have developed an in vitro coculture system i n which secretion of serotonin by a mucosal mast cell line (RBL-2H3) c an be studied at a single cell level by measuring Ca2+ transients in f ura-2 loaded mast cells and serotonin-sensitive A7r5 smooth muscle cel ls using fluorescence video microscopy and digital image processing. A 7r5 cells elevate intracellular Ca2+ via 5HT(2) receptors in response to bath-applied serotonin with an ED(50) for serotonin of 550nM. Cross linking IgE receptors with antigen caused Ca2+ transients in the mucos al mast cells. Ca2+ responses in the smooth muscle were detected appro ximate to 30-240 sec after the initiation of the mast cell Ca2+ respon ses. Smooth muscle Ca2+ responses were dependent on preloading mast ce lls with serotonin and were blocked by the 5HT(2) antagonist ketanseri n. The timing and magnitude of the smooth muscle responses indicated t hat secretion from mast cells can lead to focal concentrations of sero tonin in the range of 300 nM within 1 min of antigen stimulation. Th i s coculture technique has allowed the first direct demonstration of se rotonin-mediated signaling between immune cells and vascular elements. (C) 1994 Wiley-Liss, Inc.