Comparative Pharmacological Studies on the A2 Adenosine Receptor Agonist 5'-n-Ethyl-carboxamidoadenosine and Its F19 Isotope Labelled Derivative

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  • Rubovszky Bálint
    Department of Biophysics and Cell Biology, University of Debrecen
  • Szentmiklósi A. József
    Department of Pharmacology and Pharmacotherapy, University of Debrecen
  • Márián Teréz
    Positron Emission Tomograph Center, Research Center for Molecular Medicine, University of Debrecen PET Study Group of The Hungarian Academy of Sciences
  • Cseppento Ágnes
    Department of Pharmacology and Pharmacotherapy, University of Debrecen
  • Gesztelyi Rudolf
    Department of Pharmacology and Pharmacotherapy, University of Debrecen
  • Székely Andrea
    Department of Biophysics and Cell Biology, University of Debrecen
  • Fórizs Fruzsina
    Department of Biophysics and Cell Biology, University of Debrecen
  • Gáspár Rezso
    Department of Biophysics and Cell Biology, University of Debrecen
  • Trón Lajos
    Positron Emission Tomograph Center, Research Center for Molecular Medicine, University of Debrecen PET Study Group of The Hungarian Academy of Sciences
  • Krasznai Zoltán
    Department of Biophysics and Cell Biology, University of Debrecen

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Adenosine receptors are expressed in various mammalian tissues where they mediate the effects of adenosine on cellular functions through a number of signalling mechanisms. 18F-NECA is the positron-emitting derivative of the A2-receptor agonist NECA (5'-n-ethyl-carboxamidoadenosine) and is a radioligand for PET imaging of adenosine receptors. Contractility and relaxation studies were performed on guinea pig atrial myocardium, pulmonary artery, and thoracic aorta to compare the pharmacological effects of NECA and F-NECA (a non-emitting derivative) on tissues. Furthermore, the effect of NECA and F-NECA on the potassium conductance was investigated in DDT1 MF-2 smooth muscle cells with the patch-clamp technique. Both NECA and F-NECA reduced the contractile force in atrial myocardium and evoked phasic contraction in pulmonary artery (A1 adenosine-receptor-mediated actions) in a dose dependent manner; however, the apparent affinity was lower for F-NECA. No difference was found in relaxation induced by these compounds in 1 μM noradrenaline-precontracted aorta and pulmonary artery (in the presence of DPCPX, an A1 adenosine receptor antagonist, tissue containing A2B adenosine receptors). NECA (5 μM) and F-NECA (5 μM) also decreased the peak current and accelerated activation and inactivation properties of the potassium channels, but F-NECA was less effective. These results suggest that while NECA and F-NECA are equivalent agonists of vascular A2B receptors, they mediate different changes of some parameters. When evaluating the data obtained by the use of radiolabelled ligands, one has to take into consideration the possible physiological effects of the ligands besides its binding properties to tissues.<br>

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