Ability of SK&F 104078 and SK&F 104856 to identify alpha-2 adrenoceptor subtypes in NCB20 cells and guinea pig lung.
Alpha-2 adrenoceptors were characterized in three tissue culture cell lines and in membrane homogenates of guinea pig lung via the ability of a series of alpha adrenoceptor antagonists to inhibit the binding of [3H]clonidine, [3H]UK-14,304 and [3H]rauwolscine. The cells studied included those known to possess receptors of alpha-2A (HT29) and alpha-2B (NG108-15) subtypes as well as the previously uncharacterized NCB20 cells. Correlation of the ability of the antagonists to inhibit [3H]clonidine or [3H]UK-14,304 binding did not identify alpha-2 adrenoceptor subtypes. On the other hand, correlation of antagonist affinities against [3H]rauwolscine binding showed HT29 cells and guinea pig lung to have similar characteristics (r = 0.911) as did NG108-15 and NCB20 cells (r = 0.985). These data suggest subtle differences in the binding of [3H]agonists and [3H]antagonists to the alpha-2 adrenoceptor, resulting in the failure of [3H]clonidine and [3H]UK-14,304 to recognize differences between alpha-2A and alpha-2B receptor subtypes. 6-chloro-9-[(3-methyl-2-butenyl)oxy]-3-methyl-1H-2,3,4,5-tetrahydro-3- benzazepine (SK&F 104078) did not differentiate between the alpha-2A and alpha-2B receptor subtypes. However, 2-vinyl-7-chloro-3,4,5,6-tetrahydro-4-methylthieno[(4,3,2ef] [3]benzazepine (SK&F 104856), which has similar selectivity in functional in vitro models, was about 35-fold more potent in displacing [3H]rauwolscine binding to the alpha-2B site. These data provide additional evidence that the functional subclassification of alpha-2 adrenoceptors based on sensitivity to SK&F 104078 and SK&F 104856 subdivides this receptor in a different manner than does the alpha-2A/alpha-2B subclassification scheme.
Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania.
M M
MM
Gleason
J P
JP
Hieble
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000378:metabolism*; D000068438:Brimonidine Tartrate; D002478:Cells, Cultured; D003000:Clonidine / Q000378:metabolism; D006224:Cricetinae; D003984:Dibenzazepines / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism; D007211:Indoles; D054833:Isoindoles; D008168:Lung / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010109:Oxymetazoline / Q000378:metabolism; D011810:Quinoxalines / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000145:classification / Q000378:metabolism*; D014316:Tritium; D014407:Tumor Cells, Cultured; D015016:Yohimbine / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D001552:Benzazepines; D003984:Dibenzazepines; D007093:Imidazoles; D007211:Indoles; D054833:Isoindoles; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; C054935:SK&F 104078; C072126:BRL 41992; C071739:SK&F 104856; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D010109:Oxymetazoline; D003000:Clonidine; C072125:BRL 44408