Specific binding of leukotriene C4 to ileal segments and subcellular fractions of ileal smooth muscle cells.

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Abstract
A specific high-affinity receptor for leukotriene C4 (LTC4) has been identified on segments of longitudinal smooth muscle from guinea pig ileum, in disrupted cells obtained from the ileal segments, and in subcellular fractions enriched for mitochondrial membranes and plasma membranes, respectively. Specific [3H]LTC4 binding at a fixed input at 4 degrees C reached a plateau at 60 min with each of the four preparations and was greater than 80% reversible after binding reached equilibrium by the introduction of excess unlabeled homoligand. LIGAND analysis demonstrated a single high-affinity receptor on the smooth muscle segments, the disrupted cells, and the subcellular fractions enriched for mitochondrial membranes and for plasma membranes with respective Kd values of 7.6 nM, 1.3 nM, 13 nM, and 8.5 nM. These Kd values overlap with the concentration of LTC4 known to elicit a spasmogenic response in the ileal muscle, indicating that the radioligand recognizes a receptor that mediates the biological response. Competition analysis with disrupted ileal cells and subcellular fractions with a fixed input of LTC4 radioligand and incremental concentrations of the natural sulfidopeptide leukotrienes demonstrated leukotriene D4 (LTD4) to be 1-3 logarithms less active than LTC4 and leukotriene E4 (LTE4) to be essentially inactive. Thus, ileal longitudinal smooth muscle cells possess a high-affinity receptor that is selective for LTC4 and that receptor exhibits both a plasma membrane and subcellular distribution.

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