Abstract
Leukotrine C 4 (LTC 4), one of the major constituents of the slow reacting substance of anaphylaxis, induced a dose-dependent hydrolysis of phosphoinositides in [ 3H]inositol-prelabeled rat basophilic leukemia (RBL-1) cells. The EC 50 for LTC 4 to elicit the half maximum accumulation of [ 3H]inositol phosphates (IPs) was around 20 nM. The increase in the formation of [ 3H]inositol bisphosphate (IP 2) and [ 3H]inositol trisphosphate (IP 3) was detectable at 2 min after the stimulation and progressed up to 30 min. Accumulation of [ 3H]inositol monophosphate (IP 1) was observed only during the late phase of 5–30 min in the presence of LiCl. When cells were stimulated with LTC 4 and LTD 4 together, there was no additive accumulation in [ 3H]IPs. Pretreatment of cells with either LTC 4 or LTD 4 resulted in a decrease in production of [ 3H]IPs on further stimulation with the same agonist. The desensitization appeared to be heterologous since pretreatment of cells with LTC 4 attenuated the responsiveness to LTD 4. Conersely, pretreatment with LTD 4 also diminished the responsiveness to LTC 4 markedly. These results suggest that both LTC 4 - and LTD 4 -induced hydrolysis of phosphoinositides are mediated through the same effector in RBL-1 cells.
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