Non-adrenergic binding sites for the "alpha 2-antagonist" [3H] idazoxan in rabbit urethral smooth muscle.
In the present study, we have provided evidence that [3H] rauwolscine and [3H] idazoxan bind to different sites in rabbit urethra. The [3H] idazoxan capacity and affinity was 215 +/- 14 fmol/mg protein and 1.59 +/- 0.16 nM while [3H] rauwolscine binding parameters were 45.9 +/- 3.4 fmol/mg protein and 2.39 +/- 0.27 nM. [3H] idazoxan specific binding was inhibited only by compounds possessing an imidazoli(di)ne or a guanidinium moiety, while [3H] rauwolscine specific binding was inhibited by phenylethanolamines and classical alpha 2-antagonists. [3H] idazoxan was inhibited by KCl in a competitive and by MnCl2 in a non-competitive way, while other cations such as Na+, Li+ and Mg2+ did not inhibit [3H] idazoxan binding. Moreover, we investigated the regional distribution of [3H] idazoxan and [3H] rauwolscine along the rabbit urethra using quantitative autoradiography. Analysis of the films revealed a different distribution of these two binding sites on the urethral sections.
Yablonsky
F
F
Laboratoires Debat, Hôpital Necker, Paris, France.
Lacolle
J Y
JY
Dausse
J P
JP
D000317:Adrenergic alpha-Antagonists / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D002412:Cations / Q000494:pharmacology; D004146:Dioxanes / Q000378:metabolism*; D019329:Idazoxan; D066298:In Vitro Techniques; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D014521:Urethra / Q000378:metabolism; D015016:Yohimbine / Q000378:metabolism
D000317:Adrenergic alpha-Antagonists; D002412:Cations; D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D011955:Receptors, Drug; C064580:idazoxan receptor; D015016:Yohimbine; D019329:Idazoxan