title: Alpha-adrenergic receptors in rat myocardium. Identification by binding of [3H]dihydroergocryptine.
abstract: [3H]Dihydroergocryptine ([3H]DHE) binds to sites in membranes derived from rat myocardium that have the characteristics expected of alpha-adrenergic receptors. The binding is saturable with 41 fmol [3H]DHE bound per mg of protein and of high affinity with KD = 2.9 nM. The binding is rapid and readily reversible. Adrenergic agonists compete with [3H]DHE for binding in the order: epinephrine greater than norepinephrine greater than isoproterenol; and adrenergic antagonists compete for binding in the order: phentolamine greater than propranolol. For comparison, (-)[3H]dihydroalprenolol [(-)[3h]dha] was used to bind to sites in the same membrane preparations having characteristics of beta-receptors. The number and affinity of beta-receptors were quite similar to those of the alpha-receptors with 46 fmol (-)[EH]DHA per mg protein bound at saturation and KD = 2.5 nM. These techniques allowed identification of both beta- and alpha-adrenergic receptors in membranes derived from isolated atria, right ventricular free walls, and left ventricles including interventricular septa. This is the first report documenting direct identification of myocardial alpha-receptors by radioligand-binding techniques and complements the literature previously reporting myocardial inotopic and electrophysiological responses to alpha-adrenergic stimulation.
mesh_terms: D000526:Alprenolol / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D004088:Dihydroergotoxine / Q000378:metabolism*; D004837:Epinephrine / Q000378:metabolism; D007545:Isoproterenol / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000032:analysis* / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D010646:Phentolamine / Q000378:metabolism; D011433:Propranolol / Q000378:metabolism; D011485:Protein Binding; D011869:Radioligand Assay; D051381:Rats; D011941:Receptors, Adrenergic / Q000032:analysis*; D011942:Receptors, Adrenergic, alpha / Q000032:analysis* / Q000378:metabolism; D014316:Tritium
chemical_list: D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D004088:Dihydroergotoxine; D000526:Alprenolol; D011433:Propranolol; D007545:Isoproterenol; D009638:Norepinephrine; D004837:Epinephrine; D010646:Phentolamine