MECHANISM OF ACTION OF LEUKOTRIENE D-4 ON GUINEA-PIG TRACHEAL SMOOTH-MUSCLE CELLS - ROLES OF CA++ INFLUX AND INTRACELLULAR CA++ RELEASE

The effects of leukotriene D-4 (LTD(4)) on the concentration of intrac ellular cytosolic free calcium ([Ca++](i)) and on phosphoinositide hyd rolysis were studied in cultured guinea pig tracheal smooth muscle cel ls. In Fura-2-loaded cells, LTD(4) (10(-9)-10(-6) M) induced concentra tion-dependent changes in [Ca++](i) consisting of a slow, transient in crease followed by a sustained phase. Preincubation of cells with LTD( 4) receptor antagonist MK-571 (10(-6) M) blocked the increase in [Ca+](i). Similarly, LTD(4)-induced inositol phosphate ([H-3]InsP(s)) synt hesis was transient, concentration-dependent and inhibited by the LTD( 4) antagonist. In the absence of extracellular Ca++, LTD(4) failed to induce [Ca++](i) increases and [H-3]InsP(s) formation. Accordingly, Ni Cl2 completely inhibited the LTD(4)-stimulated [H-3]InsP(s) synthesis. Nifedipine (10(-5) M) had a slight inhibitory effect on [Ca++](i) inc rease but significantly reduced (40-50%) the [H-3]InsP(s) accumulation . These findings indicate that LTD(4)-stimulated inositol phosphate sy nthesis and [Ca++](i) increases in tracheal smooth muscle cells are re ceptor-mediated events and are dependent on the availability of extrac ellular Ca++. It is suggested that Ca++ influx plays a major role in t he LTD(4) signal transduction mechanism.