Renzetti A R, Criscuoli M, Maggi C A
Pharmacology Research Department, Menarini Ricerche SpA., Florence, Italy.
Naunyn Schmiedebergs Arch Pharmacol. 1997 Jul;356(1):139-44. doi: 10.1007/pl00005021.
The tachykinin NK2 receptors present in membranes of rat small intestine were characterized by means of tachykinin receptor agonists and antagonists, by using the natural agonist, NKA, or the nonpeptide antagonist SR 48968, as radioligands. The affinity of the antagonists was independent of the radioligand used, whereas the NK2 receptor selective agonists showed a different binding profile according to the radioligand. In particular, when using [125I]NKA, NKA and NKA(4-10) bound to a high affinity site, whilst [beta-Ala8]NKA(4-10) and GR 64349 bound to a high and a low affinity site; the high affinity site was still detected in the presence of 100 microM GppNHp which produced a strong inhibition of the specific binding of [125I]NKA. On the other hand, when using [3H]SR 48968, NKA bound to a high affinity site, [beta-Ala8]NKA(4-10) bound to a low affinity site and NKA(4-10) and GR 64349 bound to a high and a low affinity site; in this case, the high affinity site was no longer detected in the presence of 1 microM GppNHp, which did not reduce the specific binding of [3H]SR 48968 to NK2 receptors. We interpreted these data as an indication that in the rat small intestine membranes [125I]NKA labels multiple conformations of G protein-coupled NK2 receptor which are distinguished by the use of selective receptor agonists, but not by peptide or nonpeptide antagonists.
通过使用速激肽受体激动剂和拮抗剂，以天然激动剂NKA或非肽拮抗剂SR 48968作为放射性配体，对大鼠小肠膜中存在的速激肽NK2受体进行了表征。拮抗剂的亲和力与所使用的放射性配体无关，而NK2受体选择性激动剂根据放射性配体显示出不同的结合谱。特别是，当使用[125I]NKA时，NKA和NKA(4-10)与一个高亲和力位点结合，而[β-丙氨酸8]NKA(4-10)和GR 64349与一个高亲和力位点和一个低亲和力位点结合；在存在100μM GppNHp的情况下仍能检测到高亲和力位点，GppNHp对[125I]NKA的特异性结合产生了强烈抑制。另一方面，当使用[3H]SR 48968时，NKA与一个高亲和力位点结合，[β-丙氨酸8]NKA(4-10)与一个低亲和力位点结合，NKA(4-10)和GR 64349与一个高亲和力位点和一个低亲和力位点结合；在这种情况下，在存在1μM GppNHp时不再检测到高亲和力位点，GppNHp并没有降低[3H]SR 48968与NK2受体的特异性结合。我们将这些数据解释为表明在大鼠小肠膜中，[125I]NKA标记了G蛋白偶联NK2受体的多种构象，这些构象可通过使用选择性受体激动剂来区分，但不能通过肽或非肽拮抗剂来区分。
