Abstract
The recent cloning and characterization of the human histamine H3 receptor cDNA marked a significant step toward a greater understanding of the role of this receptor in the central nervous system. We now report the cloning of the rat histamine H3receptor cDNA and demonstrate distinct pharmacological species differences. The rat cDNA clone encodes a putative 445-amino acid protein with 93% identity to the human H3 receptor. Northern blot analysis revealed a major single entity of 2.7-kb in length expressed only in brain. Transfection of the rat receptor cDNA into SK-N-MC cells conferred an ability to inhibit forskolin-stimulated cAMP formation in response to histamine and other H3agonists. N-[3H]methylhistamine saturably bound to transfected cells with high affinity (Kd = 0.8 nM). All agonists tested had low or subnanomolar Ki values similar to that for the human recombinant receptor. The antagonists thioperamide and clobenpropit also bound with high affinity (Ki = 4 and 0.4 nM, respectively). This is in contrast to the antagonist profile obtained for the human recombinant receptor that showed Ki values of 58 and 0.6 nM for thioperamide and clobenpropit, respectively. These data suggest that the low affinity of thioperamide for the human H3 receptor represents a species difference in pharmacology and not a unique pharmacological subtype. It also was found that chloroproxyfan behaved as a full agonist at the rat recombinant receptor. These findings highlight the significance of validating the pharmacology of experimental compounds at both the rat and human H3 receptors.
Footnotes
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Send reprint requests to: Timothy W. Lovenberg, R. W. Johnson Pharmaceutical Research Institute, 3210 Merryfield Row, San Diego, CA 92121. E-mail:tlovenbe{at}prius.jnj.com
- Abbreviations:
- bp
- base pair
- PCR
- polymerase chain reaction
- SSC
- standard saline citrate
- Received December 14, 1999.
- Accepted February 12, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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