title: Cation sensitivity of [125I]heat binding to alpha 1-adrenoceptors in rat cerebral cortex membranes.
abstract: The alpha 1-adrenoceptor antagonist 2-[beta-(4-hydroxyphenyl)-ethylaminomethyl] tetralone (HEAT) was radiolabeled with 125I and purified to the maximal specific radioactivity of 2200 Ci/mmol. [125 I]HEAT selectively labels alpha 1-adrenoceptors (KD approximately 0.1 nM at 30 degrees C) in rat cerebral cortex membranes. Divalent cations stimulated [125 I]HEAT binding to the alpha 1-adrenoceptors. The rank order of potencies was Ni2+ greater than Mn2+ greater than Mg2+ greater than Ca2+ approximately Sr2+. The effect of Mg2+ was mainly on the Bmax of the alpha I-adrenoceptors. Monovalent cations also stimulated [125I]HEAT binding. Maximal stimulation (up to 3-fold) was seen with Na+ (optimal concentration at approximately 150 mM). Li+ and NH4+ were less effective whereas K+ was ineffective. The stimulation of [125I]HEAT binding to alpha I-adrenoceptors by Na+ was temperature-dependent.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000378:metabolism*; D000818:Animals; D002413:Cations, Divalent; D002414:Cations, Monovalent; D002540:Cerebral Cortex / Q000378:metabolism*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D010627:Phenethylamines / Q000378:metabolism*; D051381:Rats; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D044024:Tetralones
chemical_list: D000317:Adrenergic alpha-Antagonists; D002413:Cations, Divalent; D002414:Cations, Monovalent; D010627:Phenethylamines; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; C010652:BE 2254; D012964:Sodium; D008274:Magnesium