Abstract
We have reported previously novel drug-induced inactivation and reactivation of human 5-hydroxytryptamine7 (5-HT7) receptors in a recombinant cell line. To explain these novel observations, a homodimer structure displaying protomer-protomer cross-talk was proposed. To determine whether these novel observations and interpretations are due to an artifactual G protein-coupled receptor (GPCR) mechanism unique to the recombinant cell line, we explored the properties of r5-HT7 receptors expressed by cortical astrocytes in primary culture. As in the recombinant cell line, risperidone, 9-OH-risperidone, methiothepin, and bromocriptine were found to potently inactivate r5-HT7 receptors. As in the recombinant cell line, exposure of risperidone-inactivated astrocyte r5-HT7 receptors to competitive antagonists resulted in the reactivation of r5-HT7 receptors. The potencies of the reactivating drugs closely correlated with their affinities for h5-HT7 receptors. These results indicate the novel inactivating and reactivating property of drugs is not due to an artifact of the recombinant cell line expressing h5-HT7 receptors but is an intrinsic property of 5-HT7 receptors in vitro and ex vivo. This evidence suggests that a native (nonmutated) GPCR, in its native membrane environment (cortical astrocyte primary culture), can function as a homodimer with protomer-protomer cross-talk. Homodimers may be a common GPCR structure. The experimental design used in our studies can be used to explore the properties of other GPCRs in their native forms in recombinant cells, primary cultures expressing the endogenous GPCRs, and possibly in vivo. The homodimer structure and protomer-protomer cross-talk offer new avenues of research into receptor dysfunction in disease states and the development of novel drugs.
Footnotes
This work was supported by the National Institutes of Health National Institute of Mental Health [Grant MH56650].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.069278.
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ABBREVIATIONS:
- 5-HT
- 5-hydroxytryptamine
- GPCR
- G protein-coupled receptor
- HEK
- human embryonic kidney
- HBSS
- Hanks' balanced salt solution
- TR-FRET
- time-resolved fluorescence energy transfer
- MEM
- minimum essential medium
- PBS
- phosphate-buffered saline
- SB269970
- (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride
- SB270146
- 5-chloro-N-[4-methoxy-3-(1-piperazinyl)phenyl]-3-methyl-benzo[b]thiophen-2-sulfonamide hydrochloride
- ICI169369
- 2-(2-dimethylamino ethylthio)-3-phenyl quinoline.
- Received October 8, 2010.
- Accepted November 9, 2010.
- Copyright © 2011 The American Society for Pharmacology and Experimental Therapeutics
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