The Second Intracellular Loop of the α2-Adrenergic Receptors Determines Subtype-specific Coupling to cAMP Production

• Published in: The Journal of biological chemistry 1997-04, Vol.272 (15), p.9703
• Main Authors: Johnny Näsman, Christian C. Jansson, Karl E. O. à kerman
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.15.9703

The α 2 -adrenergic receptors (α 2 -ARs), which primarily couple to inhibition of cAMP production, have been reported to have a stimulating effect on adenylyl cyclase activity in certain cases. When expressed in Spodoptera frugiperda Sf9 cells the α 2A subtype showed only inhibition of forskolin-stimulated cAMP production when activated by norepinephrine (NE), whereas the α 2B subtype displayed a biphasic dose-response curve with inhibition at low concentrations of NE and a potentiation at higher concentrations. To further investigate the subtype-specific coupling, we expressed a set of chimeric α 2A -/α 2B -ARs at similar expression levels in Sf9 cells to determine the structural domain responsible for the difference between the two subtypes. When the third intracellular loops were interchanged between α 2A and α 2B subtypes, the coupling specificity remained unchanged, indicating that this loop does not confer selectivity toward a stimulating response. A biphasic dose-response curve, typical for the α 2B subtype, could be seen when the second intracellular loop of the α 2B subtype was inserted into the α 2A subtype, suggesting that this loop is important for determining the subtype-specific coupling of α 2 -ARs to cAMP production. Site-directed mutagenesis of non-conserved amino acids in the second intracellular loop of the α 2A subtype indicated that several residues are involved in the coupling specificity.