Study of mechanisms mediating contraction to leukotriene C4, D4 and other bronchoconstrictors on guinea pig trachea

Contractions of guinea pig trachea in the absence and presence of indomethacin to LTD4 greater than LTC4 greater than K+ greater than histamine greater than acetylcholine were reduced following a 45 minute exposure of the tissues to calcium-free Krebs' solution (Ca2+-free Krebs' solution), were further reduced by a transient exposure to EGTA (1.25 mM) in Ca2+-free Krebs' solution and were virtually abolished when tested in the presence of EGTA (0.125 mM) in Ca2+-free Krebs' solution. In normal Krebs' solution (2.5 mM Ca2+) the Ca2+ entry blockers nifedipine (N) much greater than D-600 greater than verapamil (V) greater than diltiazem (D) almost completely abolished the contractions to K+ but blocked only a component of the maximum response to the other agonists. After exposure to Ca2+-free Krebs' solution for 45 minutes, any residual contractions to LTC4 & LTD4, were reversed by low concentrations of N (0.3 microM) or D-600 (2.1 microM). Leukotrienes appear to mobilize a superficial and a bound store of Ca2+ which gains entry through at least two types of Ca2+ channels (or mechanisms), one of which is blocked by N and D600. K+-induced contractions appear to be dependent on superficial and tightly bound Ca2+ but entry is solely through channels which are blocked by the Ca2+ entry blockers studied. Contraction to histamine and acetylcholine persisted following exposure of the tissues to Ca2+ free Krebs' solution but contractile activity was virtually abolished in Ca2+ free Krebs' solution containing EGTA. Residual contractions to histamine and part of the residual contractions to acetylcholine in Ca2+-free Krebs' solution were blocked by low dose N (0.3 microM) or D600 (2.1 microM). These findings suggest a major role for extracellular Ca2+ during spasmogen-induced contraction in this tissue.     

Bronchoconstrictor effects of leukotriene B4 in the guinea pig in vivo

Administration of leukotriene B4 (LTB4) to anesthetized spontaneously breathing guinea pigs either by the intravenous or aerosol route produced pronounced changes in pulmonary resistance and dynamic compliance. The effects were short lived and were completely abolished by pretreatment of animals with the cyclooxygenase inhibitor indomethacin. Histological examination of lungs following aerosol administration of LTB4 showed a pronounced neutrophil infiltration. These results confirm previous in vitro studies in which LTB4 was shown to produce contractions on guinea pig parenchymal strips indirectly by releasing thromboxane A2.     

Inhibitory effect of a peptide leukotriene antagonist ONO-1078 on LTD4- and antigen-induced thromboxane B2 production in guinea pig lungs

The effect of a peptide leukotriene receptor antagonist ONO-1078 on the production of thromboxane (Tx) B₂ induced by leukotriene (LT) D₄ and antigen challenge was examined in guinea pig lungs. LTD₄ (1–1,000 nM) induced a concentration-dependent production of TxB₂ in nonsensitized guinea pig lungs and ovalbumin challenge (0.01–100 μg/ml) produced TxB₂ and peptide leukotrienes in a concentration-dependent manner in ovalbumin-sensitized guinea pig lungs. ONO-1078 inhibited LTD₄ (100 nM)-induced TxB₂ production with the IC₅₀ value of 0.24 μM. Furthermore, ONO-1078 inhibited antigen (10 μg/ml)-induced TxB₂ production with the IC₅₀ value of 0.14 μM without effect on the production of peptide leukotrienes. These results suggest that ONO-1078 may prevent the antigen-induced production of TxB₂ through the blockade of the activation of receptors by endogenously generated peptide leukotrienes.     

In vitro and in vivo chemotaxis of guinea pig leukocytes toward leukotriene B4 and its w-oxidation products

Leukotriene B4 (LTB4), 20-OH-LTB4, and 20-COOH-LTB4 were studied for their relative activities towards guinea pig peritoneal eosinophils and neutrophils during in vitro chemotaxis in modified Boyden chambers. The leukotrienes were also injected into guinea pig skin, and the cellular infiltrate in 4 hour biopsies was evaluated histologically. Eosinophils migrated more actively than neutrophils towards LTB4 in vitro, while in vivo, more neutrophils were observed. 20-OH-LTB4 was markedly less active than LTB4 in vivo and in vitro, and 20-COOH-LTB was barely active at all. Crude ionophore-stimulated neutrophil supernatants (ECF) were more active towards eosinophils than towards neutrophils, both in vivo and in vitro, compared to the pure leukotrienes. The data confirm the potent chemotactic properties of LTB4 for eosinophils and neutrophils, with less activity of its w-metabolites.     

Evidence for inhibition of leukotriene A4 synthesis by 5,8,11,14-eicosatetraynoic acid in guinea pig polymorphonuclear leukocytes

The sensitivity of the 5-lipoxygenase to inhibition by 5,8,11,14-eicosatetraynoic acid (ETYA) is species- and/or tissue-dependent. Guinea pig peritoneal polymorphonuclear leukocytes prelabeled with [3H]arachidonic acid and stimulated with ionophore A23187 formed 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE), as well as several dihydroxy fatty acids, including 5(S),12(R)-dihydroxy-6,8,10-(cis/trans/trans)-14-(cis)-eicosatetraenoic acid. ETYA (40 microM) did not inhibit, but, rather, increased the incorporation of 3H label into 5-HETE. In contrast, ETYA markedly inhibited the formation of radiolabeled dihydroxy acid metabolites by the A23187-stimulated cells. Assay of products from polymorphonuclear leukocytes incubated with exogenous arachidonic acid plus A23187, by reverse phase high performance liquid chromatography combined with ultraviolet absorption, showed a concentration-dependent inhibition of the formation of dihydroxy acid metabolite by ETYA (1-50 microM) and an increase in 5-HETE levels (maximum of 2- to 3-fold). The latter finding was verified by stable isotope dilution assay with deuterated 5-HETE as the internal standard. Another lipoxygenase inhibitor, nordihydroguaiaretic acid, potently inhibited the formation of both 5-HETE and dihydroxy acids, with an IC50 of 2 microM. The data suggest that ETYA can inhibit the enzymatic step whereby 5-hydroperoxy-6,8,11,14-eicosatetraenoic acid is converted to leukotriene A4 in guinea pig polymorphonuclear leukocytes.     

Identification of leukotriene D4 receptor binding sites in guinea pig lung homogenates using [3H]leukotriene D4

We have characterized [3H]leukotriene D4 binding to guinea pig lung homogenates. Both biphasic dissociation kinetics and curvilinear Scatchard plots indicated the presence of [3H]leukotriene high and low affinity states of the binding sites. The rank order of potency for the competition study was leukotriene C4 = leukotriene D4 greater than leukotriene E4 much greater than arachidonic acid, and for their contractile effect on lung strips was leukotriene C4 = leukotriene D4 = leukotriene E4 much greater than arachidonic acid. FPL-55712 was the only other agent tested that inhibited binding. These results suggest that binding of [3H]leukotriene D4 to the homogenate is consistent with its binding to specific leukotriene D4 receptor sites.     

Comparative effects of platelet activating factor, leukotriene D4 and histamine on guinea pig trachea, bronchus and lung parenchyma

The myotropic effect of platelet activating factor (PAF), leukotriene D4 (LTD4) and histamine were compared on guinea pig pulmonary tissues. The initial administration of PAF induced a contraction of strips of trachea, bronchus and lung parenchyma. However subsequent injections were characterized by relaxation of trachea and bronchus and a highly reduced (if any) contraction of the parenchyma. The three tissues of the guinea pig respiratory system contracted strongly to leukotriene D4 and histamine. Indomethacin blocked PAF-induced relaxation of the trachea and bronchus and reduced the contraction of the lung parenchyma. The injection of PAF in the pulmonary circulation stimulated the release of substance(s) causing the contraction of the trachea, bronchus and parenchyma. This study suggests that PAF is not a direct agonist of bronchoconstriction.     

Effects of timolol, indomethacin, and MK-571 on bronchoconstriction to infused leukotriene D4 in guinea pigs

Continuous intravenous infusions of leukotriene D4 produced a prolonged but variable bronchoconstriction (approximately a 200% increase in lung resistance (RL) and a 50% decrease in dynamic compliance (Cdyn] in anesthetized and paralysed guinea pigs that peaked within 1-1.5 min and was followed by a somewhat smaller secondary plateau response. The overall response was delayed (time to peaks) but not significantly reduced by pretreatment with the cyclooxygenase inhibitor indomethacin (1 mg/kg), was markedly potentiated by the beta-adrenoceptor antagonist timolol (5 micrograms/kg), and was partially and completely blocked by pretreatment with 0.1 and 1.0 mg/kg, respectively, of the leukotriene D4 receptor antagonist MK-571. MK-571 prevented the response in indomethacin-treated guinea pigs but was considerably more active at preventing and reversing the potentiated responses (lower dose of leukotriene D4) in animals treated with indomethacin and timolol. Additional studies in indomethacin- and timolol-treated animals demonstrated that MK-571 was active with good duration of action by the aerosol route of administration (30 min and 4 h pretreatment). The technique of infusing leukotrienes into untreated, indomethacin-treated, and indomethacin- and timolol-treated guinea pigs is a useful method to study the action and interaction of leukotriene receptor antagonists.     

Effect of a peptide leukotriene antagonist, ONO-1078 on antigen-induced airway microvascular leakage in actively sensitized guinea pigs.

We examined the effect of ONO-1078, a peptide leukotriene antagonist, on antigen-induced airway microvascular leakage in ovalbumin-sensitized guinea pigs. When guinea pigs were pretreated with mepyramine, ovalbumin challenge increased vascular permeability to Evans blue dye in trachea, main bronchi and intrapulmonary airways. Oral administration of ONO-1078 significantly reduced microvascular leakage in intrapulmonary airways at doses more than 3 mg/kg, but not in trachea. Moreover, oral administration of ONO-1078 significantly reduced SRS-A mediated microvascular leakage into all airway tissues and was more effective in intrapulmonary airways at 3 mg/kg. Simultaneously, ONO-1078 also inhibited SRS-A mediated bronchoconstriction. On the other hand, azelastine (10 mg/kg, p.o.), an anti-asthma agent, failed to inhibit microvascular leakage into the airways. These results suggest that peptide leukotrienes may be important mediators of airway microvascular leakage, and that the inhibitory effect of ONO-1078 on antigen-induced airway microvascular leakage in addition to the blockade of bronchoconstriction may have therapeutic implications for bronchial asthma.     

Study of mechanisms mediating contraction to leukotriene C4, D4 and other bronchoconstrictors on guinea pig trachea

Contractions of guinea pig trachea in the absence and presence of indomethacin to LTD₄ > LTC₄ > K⁺ > histamine > acetylcholine were reduced following a 45 minute exposure of the tissues to calcium-free Krebs' solution (Ca²⁺-free Krebs' solution), were further reduced by a transient exposure to EGTA (1.25 mM) in Ca²⁺-free Krebs' solution and were virtually abolished when tested in the presence of EGTA (0.125 mM) in Ca²⁺-free Krebs' solution. In normal Krebs' solution (2.5 mM Ca²⁺) the Ca²⁺ entry blockers nifedipine (N) ? D-600 > verapamil (V) > diltiazem (D) almost completely abolished the contractions to K⁺ but blocked only a component of the maximum response to the other agonists. After exposure to Ca²⁺-free Krebs' solution for 45 minutes, any residual contractions to LTC₄ & LTD₄, were reversed by low concentrations of N (0.3 μM) or D-600 (2.1 μM). Leukotrienes appear to mobilize a superficial and a bound store of Ca²⁺ which gains entry through at least two types of Ca²⁺ channels (or mechanisms), one of which is blocked by N and D600. K⁺-induced contractions appear to be dependent on superficial and tightly bound Ca²⁺ but entry is solely through channels which are blocked by the Ca²⁺ entry blockers studied. Contraction to histamine and acetylcholine persisted following exposure of the tissues to Ca²⁺ free Krebs' solution but contractile activity was virtually abolished in Ca²⁺ free Krebs' solution containing EGTA. Residual contractions to histamine and part of the residual contractions to acetylcholine in Ca²⁺-free Krebs' solution were blocked by low dose N (0.3μM) or D600 (2.1 μM). These findings suggest a major role for extracellular Ca²⁺ during spasmogen-induced contraction in this tissue.     

Optical isomers of a leukotriene B4 antagonist have differential effects on granulocyte diapedesis in the guinea pig dermis.

Leukotriene B4 (LTB4) is a proinflammatory product of arachidonic acid metabolism that has been implicated in a number of inflammatory diseases. When injected intradermally into the guinea pig, LTB4 has been shown to elicit a dose-dependent infiltration of granulocytes as assessed by the level of the neutrophil marker enzyme myeloperoxidase. SC-41930 [7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)propoxy]-3,4-dihydro-8- propyl-2H-1-benzopyran-2-carboxylic acid] is a potent LTB4 receptor antagonist. When compounds were coadministered along with LTB4 (35 ng) into the dermal site, racemic SC-41930, (+)-SC-41930, and (-)-SC-41930 each inhibited granulocyte accumulation with ED50 values of 340 +/- 30, 98 +/- 5.7, and 1000 +/- 142 ng, respectively; when given intravenously inhibited with ED50 values of 0.5 +/- 0.06, 0.3 +/- 0.04, and 1.4 +/- 0.19 mg/kg, respectively; and when given intragastrically inhibited with ED50 values of 1.7 +/- 0.20, 1.4 +/- 0.23, and 3.0 +/- 0.41 mg/kg, respectively.     

Biological activity of leukotriene B4 analogs: inhibition of guinea pig eosinophil migration in vitro by the 2,6-disubstituted pyridine analogs U-75,302 and U-75,485.

A "late phase" antigen-induced bronchoalveolar eosinophilia has been demonstrated in ovalbumin sensitized guinea pigs (1,2). This in vivo response to antigen inhalation can be inhibited by a 2,6-disubstituted pyridine analog of LTB4, U-75,302(2) (3). In the present study, the mechanism of the drug action was studied by assessing the activity of U-75,302 and a second analog, U-75,485 to displace [3H]-leukotriene B4 binding at the guinea pig eosinophil membrane, as well as their action as chemoattractants or inhibitors of the directional migration of guinea pig eosinophils in vitro. Radioligand competition experiments demonstrated that both analogs interacted strongly with the high affinity LTB4 binding sites on guinea pig eosinophil membrane. Both analogs are powerful chemoattractants for guinea pig eosinophils since they induced directional migration of guinea pig eosinophils when administered alone. In addition, when the cells were treated with either analog and their chemotaxis response was measured in response to a natural chemoattractant, both U-75,302 and U-75,485 at concentrations of 0.1 to 100 microM dose dependently inhibited the LTB4 induced chemotaxis response. The EC50s obtained for U-75,302 and U-75,485 as inhibitors of LTB4 induced guinea pig eosinophil chemotaxis were estimated to be 11.5 +/- 5.5 microM and 5.4 +/- 2.5 microM respectively. Under the same conditions, they had no significant effect upon eosinophil migration induced by zymosan activated plasma at concentrations below 100 microM. We suggest that the inhibition of antigen-induced eosinophil infiltration in guinea pig airway in vivo by U-75,302 or U-75,485 may be a result of partial antagonism or desensitization at the LTB4 receptor level of guinea pig eosinophils.     

The effect of ONO-3708, a novel TxA2 receptor antagonist, on U-46619-induced contraction of guinea pig and human tracheal strips in vitro and on bronchoconstriction in guinea pigs in vivo.

The effect of (9, 11), (11, 12)-didedoxa-9 alpha, 11-alpha-dimethylmethano-11,12-methano-13,14-dihydro-13-aza-14-oxo -15-cyclo-pentyl-16, 17, 18, 19, 20-pentanor-15-epi-TxA2 (ONO-3708) on 9,11-methanoepoxy-prostaglandin H2 (U-46619)-induced contraction of airway smooth muscle in the guinea pigs and human in vitro and bronchoconstriction in guinea pigs in vivo was investigated. In in vitro experiments, ONO-3708 inhibited the U-46619-induced contraction of isolated guinea pig and human tracheal smooth muscle in a dose related fashion (guinea pig; pA2=7.78, human; pA2 = 7.43). The contractions of guinea pig tracheal muscle caused by histamine and leukotriene D4 (LTD4) were not inhibited by ONO-3708. In in vivo experiments, intravenous injection of ONO-3708 at doses between 1 and 20 mg/kg inhibited the U-46619-induced increase of airway insufflation pressure as measured by Konzett-R?ssler method. In addition, ONO-3708 inhibited the U-46619-induced increase in airway reactivity to acetylcholine. These data suggest that ONO-3708 has possible therapeutic utility for asthma in which TxA2 participates.     

Characterization of leukotriene B4 synthesis in canine polymorphonuclear leukocytes.

The synthesis and release of leukotriene B4 (LTB4) from canine polymorphonuclear leukocytes (PMNs) was characterized in terms of incubation time, temperature and effects of calcium ionophore A23187 concentrations. Maximal LTB4 concentrations were determined when canine PMNs were incubated with 10 microM A23187. Increasing LTB4 concentrations were determined through 10 min incubation. The maximal LTB4 concentrations (310 +/- 30 pg LTB4/2.5 x 10(5) cells) determined at 10 min did not change through a 55 min incubation period. Greater LTB4 concentrations were synthesized by canine PMNs at 37 degrees C (268 +/- 12 pg LTB4/2.5 x 10(5) cells) than at 25 degrees C (206 +/- 11 pg LTB4/2.5 x 10(5) cells) or 5 degrees C (59 +/- 3 pg LTB4/2.5 x 10(5) cells). The synthesis of LTB4 in canine PMNs was inhibited by incubation of the cells with either of two known lipoxygenase inhibitors, BWA4C or BW755C. BWA4C inhibited LTB4 synthesis with an approximate IC50 = 0.1 microM, whereas BW755C inhibited LTB4 synthesis with an approximate IC50 = 10 microM. These results indicate canine PMNs have the capability to synthesize large quantities of LTB4 when stimulated with calcium ionophore A23187. Furthermore, the 5-lipoxygenase inhibitors BWA4C, an acetohydroxyamic acid, and BW755C, a phenyl pyrazoline, can readily inhibit LTB4 synthesis in canine PMNs.     

Comparative effects of platelet activating factor, leukotriene D4 and histamine on guinea pig trachea, bronchus and lung parenchyma

The myotropic effect of platelet activating factor (PAF), leukotriene D₄ (LTD₄) and histamine were compared on guinea pig pulmonary tissues. The initial administration of PAF induced a contraction of strips of trachea, bronchus and lung parenchyma. However subsequent injections were characterized by relaxation of trachea and bronchus and a highly reduced (if any) contraction of the parenchyma. The three tissues of the guinea pig respiratory system contracted strongly to leukotriene D₄ and histamine. Indomethacin blocked PAF-induced relaxation of the trachea and bronchus and reduced the contraction of the lung parenchyma. The injection of PAF in the pulmonary circulation stimulated the release of substance(s) causing the contraction of the trachea, bronchus and parenchyma. This study suggests that PAF is not a direct agonist of bronchoconstriction.     

Immunological quantitation and immunohistochemical localization of leukotriene A4 hydrolase in guinea pig tissues

We prepared a highly specific polyclonal antibody against leukotriene (LT) A4 hydrolase using a recombinant human enzyme. Using this antibody, we quantified LTA4 hydrolase protein content in the cytosols of guinea pig tissues. The enzyme protein content correlated well with the enzyme activity with a correlation coefficient of 0.87. However, the enzyme activity per mg of the enzyme in the cytosols was low, particularly in the liver and adrenal gland, compared with the specific activity of the purified enzyme. These observations suggest the presence of inhibitory substances and/or inactive enzymes in the cytosols of these tissues. To determine the cellular localization of LTA4 hydrolase in tissues other than blood cells, we carried out immunohistochemical examinations of guinea pig tissues. We identified epithelial cells in the tracheobronchial system and gastrointestinal tract, smooth muscle cells in the bronchi and aorta, vascular endothelial cells, and the intestinal plexus as novel cellular sources of the enzyme in the parenchyme of the tissue. Thus, LTA4 hydrolase was widely distributed in various types of parenchymal cells in the tissues, and this observation warrants further investigations on the biological activities of LTB4 in these cells and tissues.     

Effect of inhibition of thromboxane production on the leukotriene D4-mediated bronchoconstriction in the guinea pig

Leukotriene D₄ (LTD₄) administered intravenously to anesthetized, spontaneously breathing guinea pigs elicited decreases in dynamic lung compliance (C_dyn) and airway conductance (G_AW) with a maximal response achieved at 0.5 min. Simultaneously, plasma levels of thromboxane metabolite, TxB₂, and the prostacyclin metabolite, 6-keto-PGF_1α, increased 10-fold over pre-LTD₄ levels. Pretreatment of the guinea pigs with meclofenamic acid delayed the onset of the LTD₄-induced bronchoconstriction, antagonized the magnitude of the decreases in C_dyn and G_AW, and blocked the increase in plasma TxB₂ and 6-keto-PGF_1α levels. The thromboxane synthetase inhibitor, UK 37,248, suppressed the LTD₄-induced bronchoconstriction, while it completely blocked TxB₂ production without significantly affecting 6-keto-PGF_1α. The SRS-A end organ antagonist, FPL 55712, blocked both the LTD₄-induced bronchoconstriction and the production of the arachidonic acid metabolites. These results suggest that thromboxane A₂ plays an important role in mediating part of the bronchoconstriction elicited by intravenously administered LTD₄ in the guinea pig.     

Leukotriene-induced contraction is mediated by cysteinyl leukotriene receptor CysLT1 in guinea pig fundus but by CysLT1 and CysLT2 in antrum

AimsLeukotriene D₄ (LTD₄) causes contraction of the stomach through unclear receptors. The aim of the present study is to characterize the cysteinyl leukotriene receptor (CysLT) mediating leukotriene-induced muscle contraction in the stomach.Main methodsWe measured contraction of gastric muscle strips isolated from the guinea pig fundus and antrum caused by cysteinyl leukotrienes, including LTC₄, LTD₄ and LTE₄, as well as the dihydroxy leukotriene LTB₄ in vitro.Key findingsIn both fundic and antral muscle strips, LTC₄ and LTD₄ caused marked whereas LTE₄ caused moderate, concentration-dependent contractions. In contrast, LTB₄ caused only small contraction. The relative potencies for cysteinyl leukotrienes to cause contraction in both fundus and antrum were LTC₄ = LTD₄ > LTE₄. The LTD₄-induced contraction was not affected by tetrodotoxin or atropine, suggesting that the action is not neurally mediated. The LTD₄-induced contraction in the fundus was almost abolished by the CysLT₁ selective antagonist montelukast. In contrast, the LTD₄-induced contraction in the antrum was only partially inhibited by montelukast or the dual CysLT₁ and CysLT₂ antagonist BAY u9773. This antral contraction was almost abolished by the combination of montelukast and BAY u9773, indicating enhancement of inhibition.SignificanceThe results of the present study demonstrate that cysteinyl leukotrienes LTC₄, LTD₄ and LTE₄ cause moderate to marked whereas the dihydroxy leukotriene LTB₄ causes small muscle contraction in the stomach in vitro. The leukotriene-induced contraction is mediated by CysLT₁ in fundus but by CysLT₁ and CysLT₂ in antrum.     

Binding of leukotriene C4 to rat lung fibroblasts and stimulation of collagen synthesis in vitro

Arachidonate metabolites are potent biological mediators affecting multiple cellular functions. Although prostaglandins of the E series, which are products of the cyclooxygenase pathway, have been known as inhibitors or down-regulators of fibroblast proliferation and collagen synthesis, the more recently discovered products of the 5-lipoxygenase pathway have not been as extensively investigated with regard to fibroblast function. In this study, a sulfidopeptide product of the lipoxygenase pathway, leukotriene C4 (LTC4), was examined for its ability to modulate rat lung fibroblast collagen synthesis and proliferation in vitro. The data revealed the ability of LTC4 and to a lesser extent leukotriene D4 (LTD4) to stimulate collagen synthesis in a dose-dependent (10(-11)-10(-8) M) manner without affecting cellular proliferation as determined by radiolabeled thymidine incorporation; 1 nM LTC4 caused an 85% (p less than 0.02) increase above untreated controls in [3H]proline incorporation into collagenous protein in the media, which was blocked by the putative leukotriene receptor antagonist FPL55712 (10 microM) and inhibited by cycloheximide and actinomycin D. This LTC4 stimulatory effect was slightly more specific for collagen synthesis vs noncollagenous protein synthesis but was not accompanied with any change in the collagen type composition. Binding of [3H]LTC4 to these cells was specific, reversible, and saturable, with a Kd of 1.8 +/- 0.95 nM. Under equilibrium conditions, there was an estimated 2.39 X 10(4) receptors per cell. This binding was also inhibited by 10 microM FPL55712. Competitive binding studies show specificity of this binding for LTC4 relative to LTD4 and FPL55712. Furthermore, no significant conversion of LTC4 to LTD4 or leukotriene E4 was noted during the binding studies.(ABSTRACT TRUNCATED AT 250 WORDS)