Non-adrenergic binding of [3H]atipamezole in rat kidney--regional distribution and comparison to alpha2-adrenoceptors.
1 Atipamezole (4-(2-ethyl-2,3-dihydro-1H-inden-2-yl)-1H-imidazole) was first introduced as a potent and specific alpha2-adrenoceptor antagonist, but in some tissues [3H]atipamezole identifies an additional population of binding sites, distinct from both classical alpha2-adrenoceptors and I1- and I2-imidazoline receptors identified with [3H]para-aminoclonidine or [3H]idazoxan. 2 In the present study we have characterized [3H]atipamezole binding sites in rat kidney by receptor autoradiography and membrane binding assays and determined whether they are pharmacologically identical with the previously described binding sites for [3H]para-aminoclonidine and [3H]idazoxan. [3H]RX821002 and [3H]rauwolscine were used to compare the regional distribution of alpha2-adrenoceptors to that of non-adrenergic binding sites of [3H]atipamezole. 3 Comparative autoradiographic experiments demonstrated the differential localisation of [3H]atipamezole, [3H]RX821002 and [3H]rauwolscine binding sites in rat kidney. The pattern of distribution of non-adrenergic [3H]atipamezole binding sites is clearly distinct from that of alpha2-adrenoceptors. 4 The non-adrenergic binding of [3H]atipamezole in rat kidney does not fall into any of the previously identified three classes of imidazoline receptors studied with [3H]para-aminoclonidine, [3H]idazoxan and [3H]RX821002. 5 Atipamezole had no inhibitory effect on MAO-A or MAO-B activity in renal membranes, which speaks against the involvement of MAOs in the observed radioligand binding.
Sjöholm
B
B
Department of Pharmacology and Clinical Pharmacology, University of Turku, Kiinamyllyn-katu 10, FIN-20520 Turku, Finland. birsjo@utu.fi
Lähdesmäki
J
J
Pyykkö
K
K
Hillilä
M
M
Scheinin
M
M
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001667:Binding, Competitive; D005260:Female; D019329:Idazoxan / Q000031:analogs & derivatives / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008566:Membranes / Q000201:enzymology / Q000378:metabolism; D008995:Monoamine Oxidase / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011941:Receptors, Adrenergic / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D014316:Tritium; D015016:Yohimbine / Q000378:metabolism
D007093:Imidazoles; D011941:Receptors, Adrenergic; D018341:Receptors, Adrenergic, alpha-2; C050701:atipamezole; D014316:Tritium; D015016:Yohimbine; C058525:2-methoxyidazoxan; D008995:Monoamine Oxidase; D019329:Idazoxan