Evidence against the "spare" receptor nature of alpha 2-adrenoceptors in hamster white fat cells.
After having established the alpha 2-adrenoceptor nature of the binding sites specifically labeled by the alpha 2-agonist [3H] UK 14304 in hamster adipocytes, two different approaches have been used to determine whether these alpha 2-adrenoceptors were "spare receptors". The first one, consisted to block irreversibly fractions of the receptor population by various concentrations of the alpha 2-antagonist benextramine and determine the relationship between the residual receptor occupancy by UK 14304 and the corresponding magnitude of the cellular inhibitory cyclic AMP response to the alpha 2-adrenergic component of epinephrine under conditions avoiding cyclic AMP breakdown. The second approach was a detailed comparison between alpha 2-receptor occupancy by [3H] UK 14304 and the cyclic AMP inhibitory dose-response curve to this agonist in cells incubated also under conditions avoiding cyclic AMP breakdown. These two experimental approaches clearly showed that the alpha 2-adrenoceptor of hamster adipocytes are not "spare receptors".
Dieudonne
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MN
Department of Biochemistry, Faculty of Medicine Paris-Ouest, Centre Hospitalier de Poissy, France.
Pecquery
R
R
Giudicelli
Y
Y
D000273:Adipose Tissue / Q000378:metabolism*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D000068438:Brimonidine Tartrate; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D003538:Cystamine / Q000494:pharmacology / Q000031:analogs & derivatives; D007700:Kinetics; D008297:Male; D008647:Mesocricetus; D011810:Quinoxalines / Q000378:metabolism; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D000068438:Brimonidine Tartrate; C029998:benextramine; D000242:Cyclic AMP; D003538:Cystamine