Cardiac alpha 1-adrenoceptors stimulate a high-affinity GTPase activity in sarcolemmal membranes from rabbit atrial and ventricular myocytes

Eur J Biochem. 1993 Apr 1;213(1):57-65. doi: 10.1111/j.1432-1033.1993.tb17733.x.


The interaction between cardiac alpha 1-adrenoceptors and GTP-binding regulatory proteins was characterized in isolated rabbit cardiac myocytes (thereby avoiding interference by other cell types present in the myocardium) by examining the alpha 1-adrenergic stimulation of GTPase activity in sarcolemma-enriched membrane fractions. Stimulation of membrane-associated GTPase activity in both atrial and ventricular myocyte preparations by the alpha 1-adrenergic agonists 1-noradrenaline and methoxamine (in the presence of propranolol) was observed to be both linear with time and saturable. alpha 1-adrenergic stimulation did not change the Km for GTP (0.14-0.21 microM), but increased the Vmax by 39% and 72% above basal levels in atrial and ventricular membranes, respectively. Stimulation of GTPase activity by alpha 1-agonists occurred in a concentration-dependent fashion and was blocked in the presence of the alpha-adrenoceptor antagonists phentolamine and prazosin, but not yohimbine. Prior treatment of myocytes with pertussis toxin had no effect on the alpha 1-adrenergic stimulation of GTPase activity, but inhibited stimulation by muscarinic-receptor activation with carbachol. Finally, photoaffinity labelling of an approximately 75-kDa membrane-bound protein with [alpha-32P]GTP was enhanced in the presence of the alpha 1-agonist methoxamine and abolished by addition of excess non-labelled GTP, suggesting that this GTP-binding protein may interact with cardiac alpha 1-adrenoceptors; a similar GTP-binding protein which may be coupled to alpha 1-adrenoceptors has been reported in rat liver plasma membranes (Im, M. J. & Graham, R. M. (1990) J. Biol. Chem. 265, 18944-18951).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic alpha-Antagonists / pharmacology
  • Affinity Labels
  • Animals
  • Cell Membrane / enzymology
  • Cells, Cultured
  • Enzyme Activation
  • GTP Phosphohydrolases / metabolism*
  • GTP-Binding Proteins / metabolism
  • Heart Atria
  • Heart Ventricles
  • In Vitro Techniques
  • Kinetics
  • Myocardium / cytology
  • Myocardium / enzymology*
  • Pertussis Toxin
  • Rabbits
  • Receptors, Adrenergic, alpha / drug effects
  • Receptors, Adrenergic, alpha / physiology*
  • Substrate Specificity
  • Virulence Factors, Bordetella / pharmacology


  • Adrenergic alpha-Antagonists
  • Affinity Labels
  • Receptors, Adrenergic, alpha
  • Virulence Factors, Bordetella
  • Pertussis Toxin
  • GTP Phosphohydrolases
  • GTP-Binding Proteins