Specific receptors for leukotriene C4 (LTC4) were identified on smooth muscle cells isolated from bovine anterior cerebral arteries (BACASMC) and bovine microcerebrovasculatures (BMSMC). [3H]LTC4 specific bindings to both cells at a fixed input reached the maxima at 60 min and 20 min, respectively. With incremental inputs of radioligand and a constant cell number, [3H]LTC4 specific bindings reached a plateau indicative of a saturable binding site. Analysis of Scatchard plots demonstrated a single population of high-affinity binding sites in both cells. The dissociation constant (Kd) for BACASMC was 39.2 +/- 1.3 nmol.L-1 and its Bmax was 19.3 +/- 2.1 pmol/10(6) cells. For BMSMC, Kd = 2.0 +/- 0.4 nmol.L-1, Bmax = 157 +/- 13 fmol/10(6) cells. The specific [3H]LTC4 bindings was inhibited by unlabeled LTC4, LTD4 and FPL-55712 (an SRS-A antagonist). The inhibitory rates for BACASMC were 70.4% and 35.3% by LTC4 and FPL-55712 at 1 mumol.L-1, respectively. For BMSMC the inhibitory rates were 96.9%, 73.9%, and 44.9% by LTC4, LTD4, and FPL-55712 at 10 mumol.L-1, respectively.
Animals Binding Sites