Abstract

Leukotriene (LT)B4 and LTB5 cause contraction of isolated bullfrog lung. LTB4 receptors were characterized in membranes prepared from bullfrog lung. Binding of [3H]LTB4 was maximal at 5 min and was reversible with the addition of 1000-fold excess LTB4. Scatchard analysis indicated a single class of binding sites with a Kd of 2.22 nM and a Bmax of 1228.86 fmol/mg protein. The Kd and the Bmax values in the presence of guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S) were 2.76 nM and 1289.61 fmol/mg protein, respectively. The Ki values for LTB4, LTB5 and 20(OH)-LTB4 were 5.5, 30.5 and 144.0 nM, respectively, whereas 20(COOH)-LTB4 was ineffective in preventing binding of [3H] LTB4 from 10(-9) to 10(-5) M. The peptide leukotrienes LTC4, LTD4 and LTE4 failed to inhibit the specific binding of [3H]LTB4. GTP gamma S in concentrations from 10(-10) to 10(-4) M did not affect the binding of 5 nM [3H]LTB4. Neither the mammalian LTD4 antagonist LY171883 nor the mammalian LTB4 antagonist LY255283 was an effective competitor for the bullfrog lung LTB4 receptor. In addition, sulfhydryl-modifying reagents NEM and PCMP did not affect LTB4 binding as they do in mammalian membrane preparations. The LTB4 receptor shows some differences from the described mammalian receptor. The cell type containing the LTB4 receptor remains to be determined.