ascorbic-acid and cyanopindolol

Although neutrophils and eosinophils are known to produce hypochlorous acid (HOCI) at the site of cardiac injury, the exact role of this toxic oxidant on the signal transduction mechanism in the heart is not clear. In this study, the effects of HOCI on beta-adrenoceptors, G-proteins and adenylyl cyclase activity were assessed by incubating rat heart membranes with HOCl. The basal as well as forskolin-, NaF-, 5-guanylylimidodiphosphate-, and isoproterenol-stimulated adenylyl cyclase activities were depressed by incubating cardiac membranes with HOCl. While both the density and affinity of the beta1-adrenoceptors were decreased by treatment of cardiac membranes with HOCl, the characteristics of the beta2-adrenoceptors were not modified significantly. Although cholera toxin-stimulated adenylyl cyclase activity, cholera toxin-catalyzed ADP-ribosylation and stimulatory guanine nucleotide binding protein immunoreactivity were depressed by HOCl, the pertussis toxin-stimulated adenylyl cyclase activity, pertussis toxin-catalyzed ADP ribosylation and inhibitory guanine nucleotide binding protein immunoreactivity were unaltered by HOCl. The presence of L-methionine in the incubation medium prevented the HOCl-induced alterations in adenylyl cyclase activities and characteristics of beta1-adrenoceptors. These results suggest that HOCl may be one of the factors attenuating the beta-adrenoceptor linked signal transduction mechanism in conditions such as ischemic heart disease.

Topics: Adenosine Diphosphate; Adenylate Cyclase Toxin; Adenylyl Cyclases; Adrenergic beta-Antagonists; Animals; Ascorbic Acid; Cholera Toxin; Colforsin; Dose-Response Relationship, Drug; Ethylmaleimide; GTP-Binding Proteins; Guanylyl Imidodiphosphate; Hypochlorous Acid; Immunoblotting; Isoproterenol; Lipid Peroxidation; Methionine; Myocardium; Pertussis Toxin; Pindolol; Propane; Rats; Receptors, Adrenergic; Sodium Fluoride; Virulence Factors, Bordetella

Receptor autoradiography was used in guinea-pig heart to locate binding sites for the beta-adrenoceptor ligand (-)[125I]cyanopindolol (CYP) resistant to blockade by the beta-adrenoceptor antagonist (-)-propranolol (1 microM). Highly localized binding was observed to regions closely associated with the sinoatrial node, atrioventricular node and bundle of His but was not observed on myocardial, pacemaker, conducting cells or adipose tissue. Free [125I] also bound to identical sites. Binding was enhanced in the presence of ascorbic acid but was completely inhibited by (-)-isoprenaline (100 microM), serotonin (5-HT) (10 microM) and phentolamine (10 microM).

Topics: Alprenolol; Animals; Ascorbic Acid; Binding Sites; Ethanolamines; Female; Guinea Pigs; Haloperidol; Heart Conduction System; Isoproterenol; Male; Myocardium; Peroxidase; Phentolamine; Pindolol; Propanolamines; Propranolol; Protein Binding; Receptors, Adrenergic, beta; Serotonin; Thiophenes; Trachea

We have examined some of the binding characteristics and the autoradiographic distribution of binding sites for Na125I (I-Na) in airway tissue from the guinea-pig, monkey, pig, rat, mouse and from man. Basal I-Na (100 pM) binding levels were extremely low. However, in the presence of ascorbic acid (10 microM) or dithiothreitol (10 microM), I-Na binding was markedly increased in guinea-pig trachea, with lesser increases detected in monkey and rat trachea and in monkey and human bronchus. In guinea-pig trachea, ascorbic acid-induced I-Na binding was not saturable within the concentration range 100-620 pM and could not be reduced by washout. Autoradiography revealed that in central airways, I-Na binding was localized at or near the interface of the airway epithelium and submucosa in small clusters, apparently involving one or two cells per focus. The physiological significance of these binding sites is yet to be established, although they may be involved in intracellular iodine storage.

Topics: Animals; Ascorbic Acid; Dithiothreitol; Guinea Pigs; Humans; In Vitro Techniques; Iodides; Iodine Radioisotopes; Lung; Macaca fascicularis; Mice; Mice, Inbred CBA; Muscle, Smooth; Pindolol; Protein Binding; Rats; Rats, Inbred Strains; Sodium Iodide; Species Specificity; Swine; Trachea