Radioligand Binding Characteristics of the Endothelin Receptor in the Rabbit Iris

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Author(s)

Abstract

We previously suggested the presence of functionally atypical endothelin (ET) A receptors in the rabbit iris sphincter. Here, we further characterized the ET receptor by a radioligand-receptor binding study utilizing a membrane fraction of the rabbit iris. In addition, we functionally confirm the presence of an atypical ET<SUB>A</SUB> receptor in the iris dilator similar to that in the iris sphincter. In binding experiments, [<SUP>125</SUP>I]ET-1 was completely displaced by ET-3 in a biphasic fashion, but only partially by BQ-123 and ET<SUB>B</SUB> ligands. In the presence of RES-701, ET-3 and sarafotoxin (SRTX)-b completely displaced [<SUP>125</SUP>I]ET-1 in a monophasic fashion, but with shallow slopes. Moreover, ET-1, ET-3 and SRTX-b completely displaced [<SUP>3</SUP>H]BQ-123 with IC<SUB>50</SUB> values of 0.8, 81 and 4.4 nM, respectively, but with slopes of ET-3 and SRTX-b being again shallow. In iris dilator muscles, ET-3 showed lower and SRTX-b showed higher contractile activities than ET-1. SRTX-c was inactive. BQ-123 more preferentially antagonized ET-3 and SRTX-b than ET-1, with the Schild plot slope of SRTX-b being shallow. Thus, functional experiments suggested the presence of atypical ET<SUB>A</SUB> receptors in the iris dilator similar to the iris sphincter. However, the binding experiments suggested the presence of rather typical ET<SUB>A</SUB>- and ET<SUB>B</SUB>-like receptors. Therefore, we apparently failed to show ET binding sites corresponding to functionally atypical ET<SUB>A</SUB> receptors.

Journal

  • The Japanese Journal of Pharmacology

    The Japanese Journal of Pharmacology 76(3), 289-296, 1998-03

    The Japanese Pharmacological Society

References:  27

Codes

  • NII Article ID (NAID)
    10008192035
  • NII NACSIS-CAT ID (NCID)
    AA00691188
  • Text Lang
    ENG
  • Article Type
    ART
  • ISSN
    00215198
  • NDL Article ID
    4440448
  • NDL Source Classification
    ZS51(科学技術--薬学)
  • NDL Call No.
    Z53-D199
  • Data Source
    CJP  NDL  J-STAGE 
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