ISSN:
1471-4159
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Medizin
Notizen:
Photoaffinity labeling of the D2--dopamine receptor in plasma membrane preparations of various tissues from several mammalian species was performed using the recently developed D2--dopaminergic antagonist probe [125I]N-(p-azidophenethyl)spiperone ([125I]N3--NAPS). In tissues containing D2--receptors such as the corpus striatum from rat, dog, calf, hamster, guinea pig, and rabbit as well as the anterior pituitary of rat, bovine, and hamster, the probe covalently labels a peptide of Mr= 94,000. Specificity of the labeling is typically D2--dopaminergic in character. The covalent labeling is blocked by (+)-butaclamol but not by the inactive (-) isomer. Agonists block incorporation with the order of potency: N-n-propylnorapomorphine 〉 apomorphine 〉 dopamine. The D2--selective antagonist spiperrone blocks labeling of the Mr= 94,000 peptide whereas the D1--selective antagonist SCH-23390 is ineffective. Thus, these results indicate that the ligand binding subunit of the D2--dopamine receptor resides on a Mr= 94,000 peptide in these various tissues from several species. Under conditions where proteolysis is not stringently controlled, peptides of lower Mr (32–38,000) are labeled at the expense of the Mr= 94,000 peptide. The most efficient protease inhibitor tested in these systems was EDTA, suggesting that the generation of these lower Mr receptor fragments might be the result of a metal-dependent proteolysis in the membrane preparations. In the rat neurointermediate lobe, a tissue containing D2--receptors. [125I]N3--NAPS specifically labels a major peptide of Mr± 120,000 in addition to the Mr= 94,000 peptide. This peptide may represent an unprocessed or differently processed form of the receptor or a pharmacologically similar but biochemically distinct form of the receptor in this tissue. Alternatively, the Mr= 94,000 peptide labeled in all the other tissues, even under the conditions used, may already represent a fragment of this high-Mr peptide.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1111/j.1471-4159.1986.tb02850.x
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