A highly specific radioreceptor assay (RRA) for leukotriene (LT) C4 using BC3H-1 cell membrane as a source of LTC4 receptors was developed and demonstrated its use in the measurement of calcium ionophore A23187-induced LTC4 production from purified eosinophils, neutrophils, and mononuclear cells. Unlabeled LTC4 competed for the specific [3H]LTC4 binding to the BC3H-1 cell membranes in a dose-dependent manner. Under the experimental conditions used in this study, the calculated IC50 value of unlabeled LTC4 was 27.2 ± 1.2 nM (n = 5). The sensitivity of the method for LTC4 was 0.6 pmol. The cross-reactivities of LTD4, LTE4, and FPL 55712 were negligible. The recovery of the exogenously added LTC4 with eosinophils was greater than 90% in both the presence and the absence of calcium ionophore A23187. Calcium ionophore induced 73.0 ± 17.0 ng of LTC4 production/106 eosinophils (n = 8), and this was about 20-40 times more than those from neutrophils and from mononuclear cells.
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