Possible existence of leukotriene D₄ receptors and mechanism of their signal transduction in human polymorphonuclear leukocytes

Abstract

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 [³H]-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,l-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.

Key Words:

• leukotriene receptors
• inflammation
• intracellular free Ca²⁺
• ICI 198,6 15
• second messengers
• inositol trisphosphate
• protein kinase C