title: A pertussis toxin substrate regulates alpha 1-adrenergic dependent phosphatidylinositol hydrolysis in cultured rat myocytes.
abstract: The chronotropic response of the heart to alpha 1-adrenergic catecholamines influenced by pertussis toxin under certain conditions. In view of the fact that alpha 1-adrenergic action is mediated by the phosphatidylinositol pathway of hormone action in many cells, we examined the hypothesis that alpha-adrenergic agonists stimulate phosphatidylinositol hydrolysis in cardiomyocytes and that this effect is sensitive to pertussis toxin. Addition of norepinephrine to cultured rat ventricular myocytes prelabeled with myo-[2-3H]inositol resulted in rapid and significant accumulation of inositol phosphate (IP1) and inositol biphosphate. Norepinephrine-stimulated IP1 formation was not inhibited by propranolol, but was inhibited by alpha-adrenergic antagonists with an order of potency indicating alpha 1-adrenergic receptor subselectivity: prazosin (alpha 1; 3 nM) greater than yohimbine (alpha 2; 10 microM). The effect of norepinephrine to enhance IP1 formation was markedly attenuated in cells pretreated with pertussis toxin. Pertussis toxin also induced the transfer of ADP-ribose from NAD to a 41,000-dalton membrane protein in these cells. The concentration of pertussis toxin resulting in maximal inhibition of norepinephrine-stimulated IP1 formation correlated well with the concentration of pertussis toxin necessary to completely ADP-ribosylate a 41,000-dalton membrane protein (1 ng/ml). The range over which pertussis toxin inhibited norepinephrine-dependent IP1 formation and ADP-ribosylated the 41,000-dalton substrate was virtually identical. These observations establish a role for a 41,000-dalton pertussis toxin substrate in coupling the alpha 1-adrenergic receptor to phosphoinositol hydrolysis in myocardial cells.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D006321:Heart / Q000187:drug effects; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D000317:Adrenergic alpha-Antagonists; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D010566:Virulence Factors, Bordetella; D009243:NAD; C002647:inositol 1-phosphate; D000246:Adenosine Diphosphate Ribose; D037342:Pertussis Toxin; D009638:Norepinephrine