Irreversible binding of the fluorescent beta-adrenoceptor probes alprenolol-NBD and pindolol-NBD to specific and non-specific binding sites.
The fluorescent 4-nitrobenzo-2-oxa-1,3-diazolyl (NBD) derivatives of alprenolol and pindolol bind irreversible to beta-adrenoceptors and non-receptor binding sites. This was established in functional experiments on the guinea pig right atrium and trachea smooth muscle, and by radioligand binding assay of beta-adrenoceptors on Chang liver cells in culture. The pD2'-values of alprenolol-NBD and pindolol-NBD for the beta-adrenoceptors on the right atrium were: 8.3 +/- 0.1 and 8.5 +/- 0.1; on the tracheal smooth muscle strip: 8.2 +/- 0.1 and 8.8 +/- 0.1; and its pKd on Chang liver cells: 8.5 +/- 0.1 and 8.9 +/- 0.1 respectively. The results indicated that no selectivity for the beta-adrenoceptor subtypes was introduced by the addition of NBD. The irreversible binding characteristic to beta-adrenoceptors and non-receptor binding sites of the fluorescent NBD derivatives of alprenolol and pindolol makes these drugs unsuitable to label beta-adrenoceptors specifically. As the irreversible binding is introduced by the coupling of the drug with NBD, it is concluded that NBD derivatives of beta-adrenoceptor antagonists are not suitable to visualize the two-dimensional motion of beta-adrenoceptors during challenge with agonists.
Rademaker
B
B
Dept. Pharmacology, Section G.I., Weesp, The Netherlands.
Kramer
K
K
Bast
A
A
Timmerman
H
H
D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives / Q000378:metabolism*; D000526:Alprenolol / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D006325:Heart Atria; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D010069:Oxadiazoles / Q000378:metabolism*; D010869:Pindolol / Q000031:analogs & derivatives* / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism
D005456:Fluorescent Dyes; D010069:Oxadiazoles; D011943:Receptors, Adrenergic, beta; C056543:pindolol-NBD; D000526:Alprenolol; D010869:Pindolol; D009327:4-Chloro-7-nitrobenzofurazan; D007545:Isoproterenol