Characterization of human recombinant α 2A ‐adrenoceptors expressed in Chinese hamster lung cells using extracellular acidification rate changes

Human α 2A ‐adrenoceptors heterologously expressed in Chinese hamster lung (CHL) fibroblasts have been characterized pharmacologically using a cytosensor microphysiometer to measure ligand‐induced extracellular acidification rate changes. In untransfected CHL cells, noradrenaline had no effect at concentrations up to 100 μ M . In α 2A ‐adrenoceptor transfected cells the rank order of agonist potency was A‐54741 (mean pEC 50 =8.96)>dexmedetomidine (8.88)>UK‐14304 (8.42)>B‐HT 920 (7.05)>noradrenaline (6.92). A‐54741, UK‐14304 and noradrenaline had the same maximum response while dexmedetomidine and B‐HT 920 behaved as partial agonists. The selective α 2 ‐adrenoceptor ligand rauwolscine antagonized acidification rate changes with an affinity independent of the agonist used; the affinity (mean pK B ) against noradrenaline was 8.43. The selective α 1 ‐adrenoceptor ligands prazosin and doxazosin (each 3 μ M ) had no effect on noradrenaline responses. Acidification rate changes induced by each agonist were abolished by pre‐treatment of cells with pertussis toxin. These data suggest that agonist‐induced acidification rate responses in CHL cells transfected with the human α 2A ‐adrenoceptor are mediated exclusively by the recombinant protein, via pertussis toxin sensitive G i/o proteins. British Journal of Pharmacology (2000) 129 , 1333–1338; doi: 10.1038/sj.bjp.0703183