IMPORTANT CONTRIBUTION OF THE METHYLENE PART OF LTB(4) TOWARD BINDING-AFFINITY TO THE LTB(4) RECEPTORS AND RISE IN INTRACELLULAR-FREE CALCIUM-CONCENTRATION

In order to examine a role of the C(16)-C(20) methylene part of leukot riene B-4(LTB(4)) toward the activation of leukocytes, we synthesized the LTB(4)-analogues in which the length of the C(16)-C(20) part of LT B(4) is varied systematically while the two hydroxyl groups at C(5) an d C(12) positions and the 6(Z),8(E),10(E) conjugated triene unit remai ned untouched. We examined their binding affinity to the LTB(4) recept ors present in the rat polymorphonuclear leukocytes (PMNLs) and their ability to raise intracellular-free calcium concentration ([Ca2+](i)) in the rat PMNLs loaded with fura-2. As the length of the chain of LTB (4) was increased or decreased one by one, the binding affinity to the LTB(4) receptors diminished, and the analogues of more than three car bon atoms shorter chain were of about three log order less activity th an LTB(4). The biological potency as assessed in [Ca2+](i) rises parar elled that of the binding affinity to the PMNL membrane. These results indicate that the C(16)-C(20) part of LTB(4) plays important role for the activity. In a similar way we prepared the LTB(4)-analogues of a different chain length between C(2)-C(4) of LTB(4) and tested their bi ological activity. We found that the C(2)-C(4) part of LTB(4) also aff ects the activity.