The role and mechanism of activation of TRP channel in mast cells

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Allergic responses are triggered by the exocytotic release of inflammatory mediators such as histamine from mast cells. Although calcium influx from extra-cellular medium is indispensable responsible for this influx is still unknown. Recently, we found that TRP (transient receptor potential) channel, which is activated b the depletion of calcium store, is expressed in mast cells. Thus, we investigated the role of TRP and its activation mechanism in this study.1. Intracellular Ca dynamics in RBL-2H3 cells with low activity of TRP.To examine the role of TRP in RBL-2H3 cells, we prepared two types of cells in which the activity of TRP is very low. One is the knock-down cell line in which the expression level of TRP1 is suppressed b anti-sense technique. The other is the dominant negative cell line in which the function of TRP1 is suppressed by the expression of truncated TRP1. In both cell lines, no significant difference on the calcium dynamics was observed. Therefore, it is suggested that TRP1 is not involved in the calcium influx, although TRP1 s expressed in mast cells.2. The effects of hapten on the intracellular Ca dynamics.Mast cells are activated by the cross-linking of IgE receptors by multi-valent antigen, and intracellular calcium increase. It is known that addition of mono-valent hapten causes dissociation of IgE receptors and decrease in calcium concentration. To investigate the activation mechanism of calciium influx, we examined the effects of hapten on thapsigargin-induced calcium increase. Hapten did not decrease the calcium increase evoked by thapsigargin. These data suggest that the activation mechanism of calcium channel is different between antigen and thapsigargin stimulation, although both stimulation deplete calcium store.