Subcellular localization of leukotriene D4 receptors in sheep tracheal smooth muscle

The distribution of [3H]leukotriene D4 [( 3H]LTD4) receptors in subcellular membrane fractions obtained from sheep tracheal smooth muscle was studied. Using differential centrifugation and discontinuous sucrose density gradient centrifugation, the subcellular membranes were separated into six fractions. The [3H]LTD4 receptor distribution profile in these fractions correlated with markers for the plasma membrane (5'-nucleotidase and alkaline phosphodiesterase) and did not correlate with markers for the mitochondria (cytochrome c oxidase and succinate-dependent cytochrome c reductase). The dissociation constant (Kd) and maximum number of binding sites (Bmax) for [3H]LTD4 binding to the receptors in the crude mixture of membranes (PII) were 0.38 +/- 0.2 nM and 77 +/- 14 fmol/mg of protein, respectively. The Kd and Bmax of [3H]LTD4 binding to the receptors in the plasma membrane-enriched fraction (FII) were 0.40 +/- 0.2 nM and 268 +/- 46 fmol/mg of protein, respectively. The specificity profile of the [3H]LTD4 receptors in the plasma membrane-enriched fraction was equivalent to that observed in the crude membrane and correlated with the agonist myotonic activities in the smooth muscle contraction assay system. Furthermore, the binding of [3H]LTD4 to the plasma membrane receptors was modulated by guanine nucleotides in a manner analogous to that observed in crude membranes, suggesting that agonist interaction with the receptors was regulated by guanine nucleotide binding protein. These results suggest that, in sheep tracheal smooth muscle, the plasma membrane is the primary location of specific LTD4 receptors.