LEUKOTRIENE C-4 RECEPTORS ON GUINEA-PIG TRACHEOCYTES

Leukotriene (LT) C-4 receptors have been characterized on freshly isol ated guinea pig tracheal epithelial cells (tracheocytes). The [H-3]LTC (4) receptor affinity was enhanced by increasing the sodium (60-160 mM ) and the magnesium (0-10 mM) concentrations. Low concentrations of ca lcium (0-3 mM) increased [H-3]LTC(4) binding, but high concentrations (3-10 mM) decreased it. The pH (6.5-8.0) had no effect on [H-3]LTC(4) binding to tracheocytes. Under our experimental conditions, binding eq uilibrium was reached after 20 min. The association and the dissociati on rate constants were estimated to be 2.75 +/- 0.25 x 10(6) M(-1). mi n(-1) and 0.093 +/- 0.008 min(-1), respectively. The K-d(35.4 +/- 8.6 nM) and the B-max values (2.4 +/- 0.6 x 10(5) receptors/cell) were det ermined by Scatchard analysis. LTB(4), LTD(4) and LTE(4) did not inhib it [H-3]LTC(4) binding to the receptors. However, the compound FPL 557 12 inhibited the binding of [H-3]LTC(4) with an IC50 value of 9.0 +/- 1.0 mu M. [H-3]LTC(4) was not metabolized during the binding assays, a s confirmed by reverse-phase high-performance liquid chromatography. T he lack of [H-3]LTC(4) binding to glutathione-S-transferase was demons trated in the presence of an excess of reduced glutathione. LTC(4) pro duced a concentration-dependent increase of free Ca++ in tracheocytes. Our results suggest that guinea pig tracheocytes possess a specific L TC(4) receptor coupled to a Ca++ signaling pathway. This LTC(4) recept or may play a key role in the epithelium-dependent responses of airway smooth muscle.