Fc epsilon receptor mediated Ca2+ influx into mast cells is modulated by the concentration of cytosolic free Ca2+ ions.

The relationship between the Fc epsilon receptor mediated stimulation of mast cells and the Ca2+ signal it induces were studied using thapsigargin (TG), a blocker of the endoplasmic reticulum Ca2+ pump. TG induced, in mucosal mast cells (RBL-2H3 line), a dose-dependent and an InsP3-independent increase in [Ca2+]i (from resting levels of 83-150 nM to 600-680 nM), and a secretory response amounting to 30-50% of that observed upon Fc epsilon RI clustering. The TG induced rise of [Ca2+]i is most probably provided by both arrest of its uptake by the endoplasmic reticulum and influx from the medium. Thus, Ca2+ influx in mast cells may be modulated by the [Ca2+]i level.