REGULATORY MECHANISM OF HISTAMINE RELEASE BY CA LCIUM : USING RAT BASOPHILIC LEUKEMIA CELL LINE

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In mast cells and basophils, the aggregation of IgE receptors initiates histamine release and consequently, causes allevgic status such as urticaria, bronchial athma and sometimes anaphylactic shock. The regulation of histamine release is important for prevention of these diseases. The roles of cytosolic calcium as a second messenger have been revealed. The increase of intracellular Ca concentration ( [Ca^<2+>] i) is introduced by two mechanisms. One is the release from the intracellular Ca stores stimulated by inositol 1,4,5-trisphosphates and another is the influx from the extracellular medium. Non-excitable cells such as blood cells have no voltage-dependent Ca channels and the mechanism of Ca influx in these cells remains unknown. Rat basophilic leukemia cells (2H3) , a tumour analogue of rat mucosal mast cells which show histamine release after stimulation with antigen are stable and provide a useful experimental model for the study of the mechanism of Ca influx and histamine release. Therefore, effects of various agents which stimulate or attenuate histamine release on [Ca^<2+>] i in 2H3 cells were investigated.1. Intracellular Ca concentration : Cytosolic calcium concentration in single 2H3 cells was measured using a Ca probe, fluo-3 with a confocal microscopy. The oscillatrory Ca signals were observed in the absence of external Ca, but quick increase of [Ca^<2+>] i occurs after addition of external Ca.2. Ca entry in 2H3 cells : Imidazole compounds such as SK&F 96365, econazole and ketoconazole suppress both Ca uptake and histamine release.3. The changes of cytoskeleton : The changes in F-actin contents were measured with NBD-phallacidin. Antigen stimulation increases F-actin assembly both in the presence and absence of external Ca^<2+>, but thapsigargin and ionomycin which increase [Ca^<2+>] i induce actin assembly only in the presence of cytosolic Ca.