Characterization of bombesin receptors using a novel, potent, radiolabeled antagonist that distinguishes bombesin receptor subtypes
Bombesin (Bn)-related peptides affect numerous cell functions; however, receptor characterization by radiolabeled ligands is limited because only radiolabeled agonists exist. In the present study we demonstrate that [D-Tyr6]Bn(6-13)methyl ester [[D-Tyr6]Bn(6-13)ME] functions as a Bn receptor antagon...
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Published in | Molecular pharmacology Vol. 43; no. 5; pp. 762 - 774 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Pharmacology and Experimental Therapeutics
01.05.1993
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Subjects | |
Online Access | Get full text |
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Summary: | Bombesin (Bn)-related peptides affect numerous cell functions; however, receptor characterization by radiolabeled ligands
is limited because only radiolabeled agonists exist. In the present study we demonstrate that [D-Tyr6]Bn(6-13)methyl ester
[[D-Tyr6]Bn(6-13)ME] functions as a Bn receptor antagonist with high affinity. The binding of both the radiolabeled agonist
125I-[Tyr4]Bn and the radiolabeled antagonist 125I-[D-Tyr6]Bn(6-13)ME to AR42J cells, murine 3T3 cells, and dispersed guinea
pig pancreatic acini was time and temperature dependent, saturable, and reversible. Binding of the antagonist more rapidly
reached equilibrium and was more rapidly reversible. Guanine nucleotides did not affect binding of the radiolabeled antagonist,
whereas guanosine-5'-(beta,gamma-imido)triphosphate decreased agonist binding by decreasing Bn receptor affinity. Acid stripping
studies demonstrated that the radiolabeled agonist, but not the antagonist, was internalized in each cell system. Bn receptor
affinities for various Bn receptor agonists or antagonists in each cell system were identical when computed from an analysis
of inhibition curves for binding of radiolabeled agonist or antagonist. However, with AR42J cells and 3T3 cells the radiolabeled
agonist demonstrated a > 2-fold higher number of Bn receptors than did the radiolabeled antagonist. Binding studies using
cell membranes, in contrast to cells, showed equal numbers of Bn receptors with either radiolabeled ligand. The radiolabeled
agonist demonstrated high affinity binding to both rat pancreatic acinar and esophageal muscularis mucosa membranes, whereas
the radiolabeled antagonist interacted with high affinity only with the gastrin-releasing peptide-preferring subtype of Bn
receptors on pancreatic tissue. These results demonstrate that 125I-[D-Tyr6]Bn(6-13)ME is a high affinity radiolabeled antagonist
that interacts specifically with Bn receptors. In contrast to the radiolabeled agonist, binding of the antagonist is not affected
by guanine nucleotides and it is not internalized, which allows quantitation of only Bn cell surface receptors. Furthermore,
the radiolabeled antagonist can distinguish Bn receptor subtypes, whereas the radiolabeled agonist does not. This ligand should
prove useful for characterizing Bn receptors as well as studying their regulation. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0026-895X 1521-0111 |