Vol. 280, Issue 3, 1357-1365, 1997

Mechanism of Action of Leukotriene D₄ on Guinea Pig Tracheal Smooth Muscle Cells: Roles of Ca⁺⁺ Influx and Intracellular Ca⁺⁺ Release

Daniela Dumitriu, Stéphane Prié, Sylvie G. Bernier, Gaétan Guillemette and Pierre Sirois

Department of Pharmacology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4

The effects of leukotriene D₄ (LTD₄) on the concentration of intracellular cytosolic free calcium ([Ca⁺⁺]_i) and on phosphoinositide hydrolysis were studied in cultured guinea pig tracheal smooth muscle cells. In Fura-2-loaded cells, LTD₄ (10⁹-10⁶ M) induced concentration-dependent changes in [Ca⁺⁺]_i consisting of a slow, transient increase followed by a sustained phase. Preincubation of cells with LTD₄ receptor antagonist MK-571 (10⁶ M) blocked the increase in [Ca⁺⁺]_i. Similarly, LTD₄-induced inositol phosphate ([³H]InsP_s) synthesis was transient, concentration-dependent and inhibited by the LTD₄ antagonist. In the absence of extracellular Ca⁺⁺, LTD₄ failed to induce [Ca⁺⁺]_i increases and [³H]InsP_s formation. Accordingly, NiCl₂ completely inhibited the LTD₄-stimulated [³H]InsP_s synthesis. Nifedipine (10⁵ M) had a slight inhibitory effect on [Ca⁺⁺]_i increase but significantly reduced (40-50%) the [³H]InsP_s accumulation. These findings indicate that LTD₄-stimulated inositol phosphate synthesis and [Ca⁺⁺]_i increases in tracheal smooth muscle cells are receptor-mediated events and are dependent on the availability of extracellular Ca⁺⁺. It is suggested that Ca⁺⁺ influx plays a major role in the LTD₄ signal transduction mechanism.