We have examined the functional significance of the naturally occurring mutation at position 64 of human β3-adrenergic receptor (β3AR), which changes the amino acid from tryptophan to arginine (W64R-β3AR). The affinities of βAR agonists for W64R-β3AR expressed in COS-7 cells were not significantly different from those for wild type β3AR. When two receptors are expressed at various expression levels, and stimulated with CGP12177A, they showed essentially the same EC50 values and maximal responses. Overexpression of Gi and Go, or the treatment with pertussis toxin did not affect the agonist-induced cAMP response, suggesting that Gi and Go did not contribute to the β3AR-induced cAMP response. However, the enhanced cAMP response was observed when W64R-β3AR was coexpressed with the adenylyl cyclase type III isoform, and stimulated by CGP12177A and isoproterenol. These results indicate that the cAMP response of W64R-β3AR can be enhanced under the particular condition that adenylyl cyclase type III was coexpressed.
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