Agonist-induced receptor internalization in Chinese hamster ovary cells stably co-expressing β₁- and β₂-adrenergic receptors

β₁- and β₂-Adrenergic receptors (β₁-AR and β₂-AR) are co-expressed in numerous tissues, for example, heart and bladder. They play a very important role in the responses of a variety of organs to sympathetic nerve stimulation. Recent studies suggest that many G protein-coupled receptors, such as β₁-AR, β₂-AR, μ opioid receptor and δ opioid receptor, can form homo- and heterooligomers. Previous studies demonstrated that the β₁-AR and β₂-AR formed dimers in living HEK 293 cells. The aim of the present study is to investigate whether such heterooligomerization affect the agonist-induced receptor internalization in the CHO-K1 cells stably co-expressing β₁-AR and β₂-AR. Using co-immunoprecipitation, we confirmed that β₁-AR and β₂-AR formed heterooligomers in the CHO-K1 cells. In cells co-expressing β₁-AR and β₂-AR, 30% of β₁-AR was internalized by isoproterenol, whereas only 20% of β₁-AR was internalized in cells expressing the β₁-AR alone. Heterooligomerization did not affect the ratio of internalized β₂-AR. Salmeterol, a specific β₂-AR agonist, broke β₁-AR/β₂-AR heterooligomers, and induced β₂-AR-specific internalization in cells co-expressing β₁-AR and β₂-AR. The present study demonstrated that heterooligomerization between β₁-AR and β₂-AR accelerates the isoproterenol-promoted internalization of the β₁-AR, and that salmeterol induces β₂-AR- specific internalization in Chinese hamster ovary (CHO) cells stably co-expressing β₁-AR and β₂-AR.