title: Binding of (-)[3H]noradrenaline to bovine membrane of the retina. Evidence for the existence of alpha 2-receptors.
abstract: (-)[3H]Noradrenaline and [3H]clonidine bind in a saturable fashion to membrane preparations of bovine retinas. The dissociation constant for (-)[3H]noradrenaline is about 26 nM and for [3H]clonidine approximately 11.7 nM. The degree of (-)[3H]noradrenaline and [3H]clonidine binding associated with subcellular fractions of the retina enriched with conventional synaptosomes is higher than with photoreceptor synaptosomes. (-)[3H]noradrenaline binding to membrane fractions of the retina is enhanced by divalent cations like calcium, magnesium and manganese, but unaffected by sodium or potassium to any significant extent. The binding sites demonstrated a high degree of pharmacological specificity, (-)noradrenaline being the most potent displacer of (-)[3H]noradrenaline, [3H]clonidine or [3H]WB 4101. Yohimbine and phentolamine, alpha 2-receptor agonists, showed a greater affinity to the [3H]ligand binding sites than prazosin or phenoxybenzamine, both known to have an affinity for alpha 1-receptors. ATP and GTP at 1 mM reduce a specific binding of [3H]noradrenaline and [3H]clonidine. It is concluded that alpha 2-type receptors exist in the bovine retina.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D003000:Clonidine / Q000378:metabolism; D004146:Dioxanes / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000378:metabolism*; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium
chemical_list: D000316:Adrenergic alpha-Agonists; D004146:Dioxanes; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D003000:Clonidine; D009638:Norepinephrine