Lack of effect of the α _2C ‐adrenoceptor Del322‐325 polymorphism on inhibition of cyclic AMP production in HEK293 cells

Background and purpose:  The α_2C‐adrenoceptor has multiple functions, including inhibiting release of noradrenaline from presynaptic nerve terminals. A human α_2C polymorphism, Del322‐325, a potential risk factor for heart failure, has been reported to exhibit reduced signalling in CHO cells. To further understand the role of the Del322‐325 polymorphism on receptor signalling, we attempted to replicate and further study the reduced signalling in HEK293 cells.

Experimental approach:  Human α_2C wild‐type (WT) and Del322‐325 adrenoceptors were stably transfected into HEK293 cells. Radioligand binding was performed to determine affinities for both receptors. In intact cells, inhibition of forskolin‐stimulated cyclic AMP production by WT and Del322‐325 clones with a range of receptor densities (200–2320 fmol·mg⁻¹ protein) was measured following agonist treatment.

Key results:  Noradrenaline, brimonidine and clonidine exhibited similar binding affinities for WT and Del322‐325. Brimonidine and clonidine also had similar efficacies and potencies for both receptors for the inhibition of cyclic AMP production at all receptor densities tested. A linear regression analysis comparing efficacy and potency with receptor expression levels showed no differences in slopes between WT and Del322‐325.

Conclusions and implications:  The α_2C WT and Del322‐325 adrenoceptors exhibited similar binding properties. Additionally, inhibition of cyclic AMP production by Del322‐325 was similar to that of WT over a range of receptor densities. Therefore, in intact HEK293 cells, the α_2C‐Del322‐325 polymorphism does not exhibit reduced signalling to adenylyl cyclase and may not represent a clinically important phenotype.