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Departments of 1 Physiology and 2 Surgery, University of Kentucky College of Medicine, Lexington, Kentucky 40536
Adenosine A2a receptors are
found in coronary vascular tissue although, their presence in
myocardium is subject to investigation. Although there have
been numerous studies on adenosine A2a receptor agonist
effects on contractility and cAMP levels in ventricular myocytes, these
have yielded conflicting results. Negative pharmacological studies have
even led to the conclusion that A2a receptors are not
present in cardiac myocytes. The purpose of this study was to determine
whether A2a receptors are expressed in rat ventricular myocytes and what physiological effects are mediated via activation of
these receptors. Western blot analysis with a polyclonal antibody raised against a peptide sequence specific to the carboxy terminus of
the A2a receptor revealed the presence of a band at ~45
kDa. However, the immunoreactivity was located in the nonmembrane
fraction of the cell lysate. The membrane fraction only exhibited
an immunoreactive band 
50 kDa. Treatment of isolated
myocytes with the adenosine A2a agonist
2-[4-[(2-carboxyethyl)-phenyl]ethylamino]-5'-N-ethylcarboxamidoadenosine (CGS-21680) exerted no effects on cAMP levels or myocyte
twitch amplitude. These results indicate that although rat ventricular myocytes appear to express adenosine A2a receptors,
stimulation with an A2a agonist exerts no functional
effects, possibly because of the subcellular localization of the
A2a receptor.
phosphodiesterase inhibitor; Western blot
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