POSSIBLE EXISTENCE OF LEUKOTRIENE-D4 RECEPTORS AND MECHANISM OF THEIR SIGNAL TRANSDUCTION IN HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Previous work from this laboratory has demonstrated that stimulation of human polymorphonuclear leukocytes (PMN) with the peptidyl leukotriene D4 (LTD4) results in the formation of second messenger signals, i.e. mobilization of intracellular free Ca2+ ([Ca2+]i) and hydrolysis of phosphoinositides (PIP2). Based on these earlier results we have employed radioligand binding techniques to study the presence of LTD4 receptors in intact human PMN leukocytes. The binding of [H-3]-LTD4 to LTD4 receptors is rapid, reversible, specific and saturable. Scatchard analysis of the binding data indicates the presence of 116-275 identical receptors per neutrophil with an apparent dissociation constant (K(D)) of 1,1-2,3 nM. Only one class of binding sites was identified. The LTD4 receptors are located in the plasma membrane and are specific for LTD4 since binding is unaffected by other leukotrienes. Furthermore, LTD4 induces a rapid and persistent translocation of Protein Kinase C (PKC) from the cytosol to the membrane. The LTD4 binding and PKC translocation could be blocked in a concentration dependent manner by the new and specific LTD4 receptor antagonist ICI 198,615. These observations strongly suggest that human PMN might possess specific LTD4 receptors which are coupled to the inositol trisphosphate pathway resulting in a rise in the cytoplasmic free Ca2+ and redistribution of protein kinase C. A mechanism of signal transduction for leukotriene D4 is proposed.