Abstract
We have previously reported novel drug-induced inactivation and re-activation of h5-HT7 receptors in a recombinant cell line. In order to explain these novel observations, a homodimer structure displaying protomer-protomer crosstalk was proposed. In order to determine if these novel observations and interpretations are due to an artifactual 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 bromocryptine 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 re-activation of r5-HT7 receptors. The potencies of the re-activating drugs closely correlated with their affinities for h5-HT7 receptors. These results indicate the novel inactivating and re-activating 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 (non-mutated) GPCR, in its native membrane environment (cortical astrocyte primary culture), can function as a homodimer with protomer-protomer crosstalk. Homodimers may be a common GPCR structure. The experimental design employed in our studies can be utilized 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 crosstalk offer new avenues of research into receptor dysfunction in disease states and the development of novel drugs.
- Serotonin
- Gs family
- Adenylyl cyclases
- cAMP
- Desensitization/uncoupling
- Anti-depressants
- Anti-psychotics
- Drug tolerance/dependence
- Received October 8, 2010.
- Revision received November 8, 2010.
- Accepted November 9, 2010.
- The American Society for Pharmacology and Experimental Therapeutics